用境外服务器做网站,发卡网站建设,网站如何做好内链,百度一下你就知道了 官网mysql的理论依据没找到#xff0c;个人理解是先执行where的过滤条件#xff0c;先关联再过滤明显做的是无用功。oracle中倒是能在执行计划中看到#xff0c;先执行的是过滤条件(下面代码中最后一行)。explain plan for SELECT * FROM tmp_t2 t2 LEFT JOIN tmp_t1 t1 ON t2.i…mysql的理论依据没找到个人理解是先执行where的过滤条件先关联再过滤明显做的是无用功。oracle中倒是能在执行计划中看到先执行的是过滤条件(下面代码中最后一行)。explain plan for SELECT * FROM tmp_t2 t2 LEFT JOIN tmp_t1 t1 ON t2.id t1.id AND t1.good_id A-----------------------------------------------------------------------------| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |-----------------------------------------------------------------------------| 0 | SELECT STATEMENT | | 3 | 147 | 6 (0)| 00:00:01 ||* 1 | HASH JOIN | | 3 | 147 | 6 (0)| 00:00:01 || 2 | TABLE ACCESS FULL| TMP_T2 | 3 | 60 | 3 (0)| 00:00:01 ||* 3 | TABLE ACCESS FULL| TMP_T1 | 3 | 87 | 3 (0)| 00:00:01 |-----------------------------------------------------------------------------Predicate Information (identified by operation id):---------------------------------------------------1 - access(T2.IDT1.ID)3 - filter(T1.GOOD_IDA)
