AI代码解释 DELIMITER//CREATEDEFINER=`root`@`localhost`FUNCTIONrand_string2(nINT)RETURNSVARCHAR(255)CHARSETutf8mb4COLLATEutf8mb4_general_ci #该函数会返回一个字符串BEGINDECLAREchars_strVARCHAR(100)DEFAULT'abcdefghijklmnopqrstuvwxyzABCDEFJHIJKLMNOPQRSTUVWXYZ';DECLAREreturn_strVARCHAR(255)DEFAULT'';DECLARE...
(s1.common_field = 'a') and (s1.key1 is not null)) (cost=1039.45 rows=1015) -> Table scan on s1 (cost=1039.45 rows=10152) -> Single-row index lookup on s2 using idx_key2 (key2=s1.key1), with index condition: (cast(s1.key1 as double) = cast(s2.key2 as double)) (...
ref is used if the join uses only a leftmost prefix of the key or if the key is not a PRIMARY KEY or UNIQUE index (in other words, if the join cannot select a single row based on the key value). If the key that is used matches only a few rows, this is a good join type. r...
case T_FunctionScan: { FunctionScan *fscan = (FunctionScan *) plan; /* Assert it's on a RangeFunction */ Assert(rte->rtekind == RTE_FUNCTION); /* * If the expression is still a function call of a single * function, we can get the real name of the function. * Otherwise, punt...
cannotselecta single row based on the key value). If the key that is used matches only a few rows, this is a goodjointype. ref can be usedforindexed columns that are compared using the = or <=> operator. In the following examples, MySQL can use a ref ...
|1| SIMPLE |testa| const |PRIMARY,idx_name| PRIMARY |4| const |1| NULL |+---+---+---+---+---+---+---+---+---+---+1rowinset# 下面虽然name有索引,但是查询的列cusno没有索引,这时mysql计划possible_keys有索引,但实际key未走索引,若果cusno换成有索引的列,参照下面。mysql> expl...
For traditional EXPLAIN: output a single EXPLAIN row. Implements Explain_format.◆ is_hierarchical()bool Explain_format_JSON::is_hierarchical ( ) const inlineoverridevirtual A hierarchical text or a plain table. Return values true Formatter produces hierarchical text false Traditional explain Im...
1 row in set (0.00 sec) mysql> explain select * from user whereUser='root' \G *** 1. row*** id: 1 select_type: SIMPLE table: user type: ALL possible_keys: NULL key: NULL key_len: NULL ref: NULL rows: 7 Extra: Using where 1 row...
DFESplitByGroup – Splits each single input chunk from one incoming edge into smaller output chunks corresponding to row groups identified by row ids from the corresponding input chunk from the other incoming edge. DFESplitChunks – Splits each single input chunk into smaller output chunks (inverse...
valueIN(SELECTprimary_keyFROMsingle_tableWHEREsome_expr) unique_subquery is just an index lookup function that replaces the subquery completely for better efficiency. unique_subquery是一个索引查找函数,代替子查询提高效率。 index_subquery This join type is similar to unique_subquery. It replaces IN ...