OceanBase database: support NULL type (Draft)

subject

https://github.com/OceanBase-Partner/lectures-on-dbms-implementation/blob/main/miniob-topics.md

debugging

Less record

breakpoint set --file condition_filter.cpp --line 388

breakpoint set --file condition_filter.cpp --line 270

breakpoint set --file bplus_tree.cpp --line 2467



Query index
IndexScanner *Table::find_index_for_scan

IndexScanner *BplusTreeIndex::create_scanner
BplusTreeScanner::open
find_first_index_satisfied
breakpoint set --file bplus_tree.cpp --line 190
}

Table::scan_record

scan_record_by_index

next_entry

get_next_idx_in_memory
filter->filter
bool BplusTreeScanner::satisfy_condition

breakpoint set --file bplus_tree.cpp --line 2283


breakpoint set --file tuple.cpp --line 531

breakpoint set --file tuple.cpp --line 602


breakpoint set --file bplus_tree.cpp --line 2274

breakpoint set --file bplus_tree.cpp --line 2309


breakpoint set --file bplus_tree.cpp --line 190

breakpoint set --file tuple.cpp --line 531


breakpoint set --file condition_filter.cpp --line 105


breakpoint set --file execute_stage.cpp --line 811


breakpoint set --file execute_stage.cpp --line 722


case SCF_INSERT:

breakpoint set --file default_storage_stage.cpp --line 180


breakpoint set --file execute_stage.cpp  --line 340


breakpoint set --file tuple.cpp --line 586


breakpoint set --file condition_filter.cpp --line 143


breakpoint set --file condition_filter.cpp --line 105


breakpoint set --file execute_stage.cpp --line 811


breakpoint set --file execute_stage.cpp --line 722




IndexScanner *Table::find_index_for_scan(const DefaultConditionFilter &filter)


breakpoint set --file bplus_tree.cpp --line 190


breakpoint set --file table.cpp --line 1006


bool BplusTreeScanner::satisfy_condition(const char *pkey)

breakpoint set --file bplus_tree.cpp --line 2270

breakpoint set --file bplus_tree.cpp --line 1991

difficulty

1.5

Q: multi table query, case: select t12.num,t13.num,t12.birthday from t12,t13 where t12.num=t13.num; select t12.num,t13.num,t12.birthday when displaying. How do you handle it? The default code is displayed according to the table filter field?

f7327f5bb81fada1d222df3b9e8a82e6.png

1.4gdb compare the search difference between ordinary index and null index

Tip 1: how do operators solve case less before faster full set search_ EQUAL: ｜｜ case NOT_EQUAL: ｜｜

Tip 2: difference of comparison operator select * from t12 where num =14; select * from t12 where num is null;

Query index
IndexScanner *Table::find_index_for_scan

IndexScanner *BplusTreeIndex::create_scanner
BplusTreeScanner::open
find_first_index_satisfied
breakpoint set --file bplus_tree.cpp --line 190
}

Table::scan_record

scan_record_by_index

next_entry

get_next_idx_in_memory
filter->filter
bool BplusTreeScanner::satisfy_condition

breakpoint set --file bplus_tree.cpp --line 2283

I gdb track errors: why is the data wrong. It was found that:

breakpoint set --file condition_filter.cpp --line 388

breakpoint set --file condition_filter.cpp --line 270

breakpoint set --file bplus_tree.cpp --line 2467

bool DefaultConditionFilter::filter(const Record &rec) const

1.3 comparison with index and comparison without index

bool DefaultConditionFilter::filter(const Record &rec) const
CompareKey
bool BplusTreeScanner::satisfy_condition(const char *pkey)

void TupleRecordConverter::add_record(const char *record)

Subtext: what do these three functions do,

1.2 null and value, operator, null comparison

Null and null true
null and other values false

1.3 how to store null instead of 999

0 == strcmp(s, "999")
How to store null in memory address? Do you use null ptr? Can't resolve is null value?

Train of thought analysis

19th test

No index, no filter condition, query

bool DefaultConditionFilter::filter(const Record &rec) const

execute_stage.cpp


breakpoint set --file execute_stage.cpp --line 342


breakpoint set --file condition_filter.cpp --line 388

breakpoint set --file condition_filter.cpp --line 388

breakpoint set --file condition_filter.cpp --line 270

breakpoint set --file bplus_tree.cpp --line 2467

8c2f3f2f0768518da9706a4dcf8cac6d.png

select NUM from NULL_TABLE3;

breakpoint set --file bplus_tree.cpp --line 2467

Key issues:

Query no record select * from NULL_TABLE3;

I began to think that it was null and there was no need to query [error]

Case: there is a problem with the avg function in the case of pure null

select * from NULL_TABLE3;

breakpoint set --file execute_stage.cpp --line 342

breakpoint set --file tuple.cpp --line 355

breakpoint set --file tuple.cpp --line 834

839

SELECT NUM FROM NULL_TABLE3;

null: result file difference(`-` is yours and `+` is base)
 CREATE TABLE NULL_TABLE3(ID INT, NUM INT NULLABLE);
 SUCCESS
 INSERT INTO NULL_TABLE3 VALUES (1, NULL);
 SUCCESS
 INSERT INTO NULL_TABLE3 VALUES (2, NULL);
 SUCCESS
 SELECT COUNT(NUM) FROM NULL_TABLE3;
 COUNT(NUM)
 0
 SELECT MIN(NUM) FROM NULL_TABLE3;
+MIN(NUM)
+NULL
+SELECT max(num) FROM null_table3;
+MAX(NUM)
+NULL
+SELECT avg(num) FROM null_table3;
+AVG(NUM)
+NULL

8f306a2f07ef2203d29b6045fdb169ad.png

18th test

2359ac666e468f2b549276eeb91efa28.png

Test 17: multi meter situation

insert into t13 values(1,20,"2021-01-30");
insert into t12 values(2,20,"2021-01-01");
select t12.num,t13.num,t12.birthday from t12,t13 where t12.num=t13.num;

breakpoint set --file execute_stage.cpp --line 308

selects

[0] = (relation_name = "t12", attribute_name = "birthday", funtype = FUN_NO) [1] = (relation_name = "t13", attribute_name = "num", funtype = FUN_NO) [2] = (relation_name = "t12", attribute_name = "num", funtype = FUN_NO)

Q: multi table query, case: select t12.num,t13.num,t12.birthday from t12,t13 where t12.num=t13.num;

select t12.num,t13.num,t12.birthday when displaying. How do you handle it? The default code is displayed according to the table filter field?

select t12.num,t13.num,t12.birthday from t12,t13 where t12.num=t13.num;

4f12ecdddfc3c75ec196989c93fe0313.png

breakpoint set --file execute_stage.cpp --line 307

breakpoint set --file execute_stage.cpp --line 270

breakpoint set --file execute_stage.cpp --line 340

breakpoint set --file execute_stage.cpp --line 362

1fdce6189431146436486957ee986a74.png

 schema_ = {
      fields_ = size=2 {
        [0] = {
          type_ = INTS
          table_name_ = "t12"
          field_name_ = "num"
          visible_ = true
          function_type = FUN_NO
          nullable_ = 1
          field_name_count_number_ = ""
        }
        [1] = {
          type_ = DATES
          table_name_ = "t12"
          field_name_ = "birthday"
          visible_ = true
          function_type = FUN_NO
          nullable_ = 1
          field_name_count_number_ = ""
        }
      }
      realTabeNumber = -1
    }
    
   [0] = {
    tuples_ = size=1 {
      [0] = {
        values_ = size=1 {
          [0] = std::__1::shared_ptr<TupleValue>::element_type @ 0x00007fc448604080 strong=1 weak=1 {
            __ptr_ = 0x00007fc448604080
          }
        }
        sp1 = nullptr {
          __ptr_ = nullptr
        }
        sp2 = nullptr {
          __ptr_ = nullptr
        }
        sp3 = nullptr {
          __ptr_ = nullptr
        }
        selectComareIndex = -1
      }
    }
    schema_ = {
      fields_ = size=1 {
        [0] = {
          type_ = INTS
          table_name_ = "t13"
          field_name_ = "num"
          visible_ = true
          function_type = FUN_NO
          nullable_ = 1
          field_name_count_number_ = ""
        }
      }
      realTabeNumber = -1
    }

Judge whether to adjust
adjustment

select t12.num,t13.num,t12.birthday from t12,t13 where t12.num=t13.num;

create_selection_executor
null: result file difference(`-` is yours and `+` is base)
 SELECT NULL_TABLE.NUM,NULL_TABLE2.NUM,NULL_TABLE.BIRTHDAY FROM NULL_TABLE,NULL_TABLE2 WHERE NULL_TABLE.NUM=NULL_TABLE2.NUM;
-18 | 2020-01-01 | 18
-NULL_TABLE.NUM | NULL_TABLE.BIRTHDAY | NULL_TABLE2.NUM
+18 | 18 | 2020-01-01
+NULL_TABLE.NUM | NULL_TABLE2.NUM | NULL_TABLE.BIRTHDAY

16 tests:

When there is an index: non null, null is false compared with the value, and no record can be queried? How to handle this? select * from t12 where num is not null--- There should be a record

insert into t12 values(6,null,null); //0k

select * from t12 where num =14; select * from t12 where num is null; select * from t12 where num is not null;

15 wrong

Modify: bool DefaultConditionFilter::filter

How do normal types compare to int s

gdb debugging

breakpoint set --file execute_stage.cpp --line 270

breakpoint set --file execute_stage.cpp --line 397

select * from t12 where num is not null;

1 | 2 | 2020-01-01 Lack of records

Look at the log: DefaultConditionFilter::filter IS_NOT_NULL

void TupleRecordConverter::add_record(const char *record)

Index query:

Line 1999

tmp = CompareKey(node->keys + i * file_header_.key_length, key, file_header_.attr_type, file_header_.attr_length);

case LESS_THAN:
    switch (attr_type)
    {
    case INTS:
      flag = (i1 < i2);
      break;
    case FLOATS:
      flag = (f1 < f2);
      break;
    case CHARS:
      flag = (strncmp(s1, s2, attr_length) < 0);
      break;
    case DATES:
      flag = (i1 < i2);
      break;
    default:
      LOG_PANIC("Unknown attr type: %d", attr_type);
    }
    break;

There is an error. It is wrong to compare the conditions with and without index

According to the test, I wrote the wrong code

int CompareKey(const char *pdata, const char *pkey, AttrType attr_type, int attr_length)

4 comparison code

* thread #9, stop reason = breakpoint 1.1
  * frame #0: 0x0000000109e572e4 observer`CompareKey(pdata="\U00000002", pkey="999", attr_type=INTS, attr_length=4) at bplus_tree.cpp:191:3 [opt]
    frame #1: 0x0000000109e5d05a observer`BplusTreeHandler::find_first_index_satisfied(this=0x00007ff5b1407788, compop=IS_NULL, key="\xff\xff\xff\xff", page_num=<unavailable>, rididx=0x00007ff5b2b04804) at bplus_tree.cpp:1955:13 [opt]
    frame #2: 0x0000000109e5d3cf observer`BplusTreeScanner::open(this=0x00007ff5b2b044c0, comp_op=IS_NULL, value=<unavailable>) at bplus_tree.cpp:2081:23 [opt]
    frame #3: 0x0000000109e60445 observer`BplusTreeIndex::create_scanner(this=0x00007ff5b14076e0, comp_op=IS_NULL, value="999") at bplus_tree_index.cpp:98:31 [opt]
    frame #4: 0x0000000109e76550 observer`Table::find_index_for_scan(this=0x00007ff5b1605160, filter=<unavailable>) at table.cpp:1067:31 [opt]
    frame #5: 0x0000000109e75f54 observer`Table::scan_record(this=0x00007ff5b1605160, trx=0x00007ff5b1606eb0, filter=0x00007000065b1818, limit=2147483647, context=0x00007000065b17e0, record_reader=(observer`scan_record_reader_adapter(Record*, void*) at table.cpp:502))(Record*, void*)) at table.cpp:531:33 [opt]

result:

[2021-11-13 18:44:3 pid:18738 tid:7000065b5000  INFO: /Users/wangchuanyi/code/miniob/src/observer/sql/parser/parse.cpp condition_init 195]>>left_is_attr ...........
[2021-11-13 18:44:3 pid:18738 tid:7000065b5000  INFO: /Users/wangchuanyi/code/miniob/src/observer/storage/common/bplus_tree.cpp CompareKey 197]>>CompareKey int >>>: 1=2,2=3750201
[2021-11-13 18:44:3 pid:18738 tid:7000065b5000  INFO: /Users/wangchuanyi/code/miniob/src/observer/storage/common/bplus_tree.cpp CompareKey 197]>>CompareKey int >>>: 1=2,2=3750201
[2021-11-13 18:44:3 pid:18738 tid:7000065b5000  INFO: /Users/wangchuanyi/code/miniob/src/observer/storage/common/bplus_tree.cpp CompareKey 197]>>CompareKey int >>>: 1=2,2=3750201
[2021-11-13 18:44:3 pid:18738 tid:7000065b5000  INFO: /Users/wangchuanyi/code/miniob/src/observer/storage/common/bplus_tree.cpp CompareKey 197]>>CompareKey int >>>: 1=3750201,2=3750201
[2021-11-13 18:44:3 pid:18738 tid:7000065b5000  INFO: /Users/wangchuanyi/code/miniob/src/observer/storage/common/bplus_tree.cpp CompareKey 197]>>CompareKey int >>>: 1=3750201,2=3750201
[2021-11-13 18:44:3 pid:18738 tid:7000065b5000  INFO: /Users/wangchuanyi/code/miniob/src/observer/storage/common/bplus_tree.cpp CompareKey 197]>>CompareKey int >>>: 1=3750201,2=3750201
[2021-11-13 18:44:3 pid:18738 tid:7000065b5000  INFO: /Users/wangchuanyi/code/miniob/src/observer/storage/common/bplus_tree.cpp CompareKey 197]>>CompareKey int >>>: 1=3750201,2=3750201
[2021-11-13 18:44:3 pid:18738 tid:7000065b5000  INFO: /Users/wangchuanyi/code/miniob/src/observer/sql/executor/execute_stage.cpp do_select 681]>> query resault. id | num | birthday

Why?
Null is stored according to 999 when inserting. But during the search. I didn't modify the resolution. Null is filtered according to null

//Compare the size of two key s
int CompareKey(const char *pdata, const char *pkey, AttrType attr_type, int attr_length)

bool DefaultConditionFilter::filter(const Record &rec) const

No, where does it fall

Find by index:

RC Table::scan_record(

null is represented by 999

 IndexScanner *index_scanner = find_index_for_scan(filter);
  if (index_scanner != nullptr)
  {
    return scan_record_by_index(trx, index_scanner, filter, limit, context, record_reader);
  }

1faecc37091dddb49caa28920dbbaaf6.png

2.11 - null is the opposite of null comparison rules and bought on the Internet

Modify filter conditions:

bool DefaultConditionFilter::filter(const Record &rec) const

2.10 there is an error

Title: support NULL type

sql: select * from t where null is null; -- Note = difference from is

Question: is null null true or false?

The test results are incorrect

d4eb03443d80d58b67138d2bab9c486f.png

Error code location: null is not a column and an error is reported directly
Why has NULLL changed???

e9f6fd4ac322baa76fb9d1189723bc41.png

right_is_attr = 1 right_attr = (relation_name = 0x0000000000000000, attribute_name = "NULLL", funtype = FUN_MAX | 0xe2f300a8)

24d1a4919d6dbd8c241f423396d1bf3d.png

Error sql:

select * from t12 WHERE NULL IS NULLL;

right.is_attr = true;
    const FieldMeta *field_right = table_meta.field(condition.right_attr.attribute_name);
    if (nullptr == field_right)
    {
      LOG_WARN("No such field in condition. %s.%s", table.name(), condition.right_attr.attribute_name);
      return RC::SCHEMA_FIELD_MISSING;
    }
    
    
  void condition_init(Condition *condition, CompOp comp, 
                    int left_is_attr, RelAttr *left_attr, Value *left_value,
                    int right_is_attr, RelAttr *right_attr, Value *right_value) {

|value comOp value

2.9 both the comparison operator and null comparison are false

Comparison Functions and Operators

https://dev.mysql.com/doc/refman/8.0/en/working-with-null.html

12.4.2 Comparison Functions and Operators

https://dev.mysql.com/doc/refman/8.0/en/comparison-operators.html#operator_equal

https://dev.mysql.com/doc/refman/8.0/en/working-with-null.html

mysql> SELECT 1 = NULL, 1 <> NULL, 1 < NULL, 1 > NULL;

You cannot use arithmetic comparison operators such as =, <, or <> to test for NULL. To demonstrate this for yourself, try the following query:

Because the result of any arithmetic comparison with NULL is also NULL, you cannot obtain any meaningful results from such comparisons. https://dev.mysql.com/doc/refman/8.0/en/working-with-null.html

Voice over:

If any value is compared with NULL, the result is FALSE.
If any comparison operation is NULL, the result is FALSE.

code:

bool DefaultConditionFilter::filter(const Record &rec) const

select * from t12 where 1<>NULL; select * from t12 where NULL<>1;

filter->filter(record)))

RC Table::scan_record_by_index(

class ConditionFilter {
public:
  virtual ~ConditionFilter();

  /**
   * Filter one record
   * @param rec
   * @return true means match condition, false means failed to match.
   */
  virtual bool filter(const Record &rec) const = 0;
};

[] view the select filter criteria completely

do_select->create_selection_executor->

class DefaultConditionFilter : public ConditionFilter

execute

//sql execution
RC SelectExeNode::execute(TupleSet &tuple_set) {
  CompositeConditionFilter condition_filter;
  condition_filter.init((const ConditionFilter **)condition_filters_.data(), condition_filters_.size());

  tuple_set.clear();
  tuple_set.set_schema(tuple_schema_);
  tuple_set.old_schema =old_tuple_schema;
  TupleRecordConverter converter(table_, tuple_set);
  return table_->scan_record(trx_, &condition_filter, -1, (void *)&converter, record_reader);
}

RC Table::scan_record(Trx *trx, ConditionFilter *filter, int limit, void *context, RC (*record_reader)(Record *record, void *context))
IndexScanner *index_scanner = find_index_for_scan(filter);
rc = scanner.open_scan(*data_buffer_pool_, file_id_, filter);
condition_filter_->filter(current_record))
bool DefaultConditionFilter::filter(const Record &rec) const

Summary:

If any value (reserved operator) is compared with NULL, the result is FALSE

https://dev.mysql.com/doc/refman/8.0/en/working-with-null.html

2.8 modifying index filter conditions

bool BplusTreeScanner::satisfy_condition(const char *pkey)

AttrType attr_type = index_handler_.file_header_.attr_type;

 case IS_NULL:
    {
      flag =false;
    }
    break;

    case IS_NOT_NULL:
    {
      flag =true;
    }
    break;

2.7 why is the implementation fruitless

select * from t12 where id is null; select * from t12 where id is not null;

select * from t12 where 1<>NULL; select * from t12 where 1 IS NOT NULL;

Task: RC defaultconditionfilter:: init (Table & table, const condition & condition)

[] task:

bool DefaultConditionFilter::filter(const Record &rec) const

1 IS NOT NULL; //true case IS_NOT_NULL: return cmp_result != 0;

2.6 execution error

select * from t12 where id is null;

std::vector<DefaultConditionFilter *> condition_filters;

RC DefaultConditionFilter::init(Table &table, const Condition &condition)

private:
  ConDesc  left_;
  ConDesc  right_;
  AttrType attr_type_ = UNDEFINED;
  CompOp   comp_op_ = NO_OP;
};

Task: adjust RC DefaultConditionFilter::init function

2.5 null judgment when adding query

where:
condition:

2.4 create: add NOT NULL keyword

2.3 modifying aggregate functions

bool TupleSet::avg_print(std::ostream &os) const

TupleField contains aggregate functions
std::vector<std::shared_ptr> values_;

2.2 display Tuple tuple;

Is null display the same as normal type display?
Consider the case of a single line here
//Single table aggregation: only one row
Understand class: class Tuple

code implementation

2.3 where conditions

Generate filter condition: STD:: vector < defaultconditionfilter * > condition_ filters;

RC DefaultConditionFilter::init(Table &table, const Condition &condition)

private:
  ConDesc  left_;
  ConDesc  right_;
  AttrType attr_type_ = UNDEFINED;
  CompOp   comp_op_ = NO_OP;
};

Execute filter condition
bool DefaultConditionFilter::filter(const Record &rec) const

bool BplusTreeScanner::satisfy_condition(const char *pkey)

Use 999 code

comOp:
     EQ { CONTEXT->comp = EQUAL_TO; }
    | LT { CONTEXT->comp = LESS_THAN; }
    | GT { CONTEXT->comp = GREAT_THAN; }
    | LE { CONTEXT->comp = LESS_EQUAL; }
    | GE { CONTEXT->comp = GREAT_EQUAL; }
    | NE { CONTEXT->comp = NOT_EQUAL; }
    ;

2.2 display Tuple tuple;

void TupleRecordConverter::add_record(const char *record)

test result

case 3

null: result file difference(`-` is yours and `+` is base)
 3. SELECT WITH CONSTANT
 SELECT * FROM NULL_TABLE WHERE 1 IS NULL;
-FAILURE
+ID | NUM | PRICE | BIRTHDAY
 SELECT * FROM NULL_TABLE WHERE 1 IS NOT NULL;
-FAILURE
+1 | 18 | 10 | 2020-01-01
+2 | NULL | 20 | 2010-01-11
+3 | 12 | 30 | NULL
+4 | 15 | 30 | 2021-01-31
+ID | NUM | PRICE | BIRTHDAY
 SELECT * FROM NULL_TABLE WHERE NULL=1;
-FAILURE
+ID | NUM | PRICE | BIRTHDAY
 SELECT * FROM NULL_TABLE WHERE 1=NULL;
-FAILURE
+ID | NUM | PRICE | BIRTHDAY
 SELECT * FROM NULL_TABLE WHERE 1<>NULL;
-FAILURE
+ID | NUM | PRICE | BIRTHDAY
 SELECT * FROM NULL_TABLE WHERE 1<NULL;
-FAILURE
+ID | NUM | PRICE | BIRTHDAY
 SELECT * FROM NULL_TABLE WHERE 1>NULL;
-FAILURE
+ID | NUM | PRICE | BIRTHDAY

CREATE TABLE NULL_TABLE(ID INT, NUM INT NULLABLE, PRICE FLOAT NOT NULL, BIRTHDAY DATE NULLABLE);

CREATE TABLE NULL_TABLE2(ID INT, NUM INT NULLABLE, PRICE FLOAT NOT NULL, BIRTHDAY DATE NULLABLE);

CREATE INDEX INDEX_NUM ON NULL_TABLE(NUM);

 CREATE TABLE NULL_TABLE(ID INT, NUM INT NULLABLE, PRICE FLOAT NOT NULL, BIRTHDAY DATE NULLABLE);
-FAILURE
+SUCCESS
 CREATE TABLE NULL_TABLE2(ID INT, NUM INT NULLABLE, PRICE FLOAT NOT NULL, BIRTHDAY DATE NULLABLE);
-FAILURE
+SUCCESS
 CREATE INDEX INDEX_NUM ON NULL_TABLE(NUM);
-FAILURE
+SUCCESS

3298bb857adc370ead1071015fc2060b.png

core ok

: line 1: 1355 Segmentation fault: 11 ./observer -f ./observer.ini

0x0000000107d8ef8d Table::make_record(int, _Value const*, char*&) + 1357 (table.cpp:430)

No, ok

f93af99ea8021b6cb8df592825469889.png

null: result file difference(`-` is yours and `+` is base)
 3. SELECT WITH CONSTANT
 SELECT * FROM NULL_TABLE WHERE 1 IS NULL;
 ID | NUM | PRICE | BIRTHDAY
 SELECT * FROM NULL_TABLE WHERE 1 IS NOT NULL;
 1 | 18 | 10 | 2020-01-01
 2 | NULL | 20 | 2010-01-11
 3 | 12 | 30 | NULL
 4 | 15 | 30 | 2021-01-31
 ID | NUM | PRICE | BIRTHDAY
 SELECT * FROM NULL_TABLE WHERE NULL=1;
-FAILURE
+ID | NUM | PRICE | BIRTHDAY
 SELECT * FROM NULL_TABLE WHERE 1=NULL;
 ID | NUM | PRICE | BIRTHDAY
 SELECT * FROM NULL_TABLE WHERE 1<>NULL;
-1 | 18 | 10 | 2020-01-01
-2 | NULL | 20 | 2010-01-11
-3 | 12 | 30 | NULL
-4 | 15 | 30 | 2021-01-31
 ID | NUM | PRICE | BIRTHDAY
 SELECT * FROM NULL_TABLE WHERE 1<NULL;
-1 | 18 | 10 | 2020-01-01
-2 | NULL | 20 | 2010-01-11
-3 | 12 | 30 | NULL
-4 | 15 | 30 | 2021-01-31
 ID | NUM | PRICE | BIRTHDAY
 SELECT * FROM NULL_TABLE WHERE 1>NULL;
 ID | NUM | PRICE | BIRTHDAY

Posted on Thu, 18 Nov 2021 01:55:09 -0500 by mk1200

Programmer Help

OceanBase database: support NULL type (Draft)

debugging

difficulty

1.5

1.4gdb compare the search difference between ordinary index and null index

1.3 comparison with index and comparison without index

1.2 null and value, operator, null comparison

1.3 how to store null instead of 999

Train of thought analysis

19th test

18th test

Test 17: multi meter situation

16 tests:

15 wrong

There is an error. It is wrong to compare the conditions with and without index

2.11 - null is the opposite of null comparison rules and bought on the Internet

2.10 there is an error

2.9 both the comparison operator and null comparison are false

2.8 modifying index filter conditions

2.7 why is the implementation fruitless

2.6 execution error

2.5 null judgment when adding query

2.4 create: add NOT NULL keyword

2.3 modifying aggregate functions

2.2 display Tuple tuple;

code implementation

2.3 where conditions

2.2 display Tuple tuple;

test result

case 3

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