Using Multiple Conditions with AND Similarly, you can use the AND operator to combine multiple conditions in the IF function. In this case, all conditions must evaluate to true for the value_if_true to be retur
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CASE N WHEN 1 THEN SELECT "One" WHEN 2 WHEN 3 THEN SELECT "Two or Three" ELSE SELECT "The number is outside range" CASE END; This gives a SQL syntax error. Thanks -- Jeff in Seattle Subject Written By Posted CASE with multiple consecutive WHEN(s) ...
If you do not use columns from all tables named in a query, MySQL stops scanning any unused tables as soon as it finds the first match. In the following case, assuming that t1 is used before t2 (which you can check with EXPLAIN), MySQL stops reading from t2 (for any particular row ...
使用foreachENcase when then 的基本用法 SELECT CASE WHEN b.is_leave = 0 THEN '在职' WHEN ...
("lock3",0) Implementing this option one shall take care of possible deadlocks. Also in such case we shall allow RELEASE_LOCK to release all locks which thread has. It would be also convenient to be able to get list of locks which current thread owns for debugging purposes. Current task...
•SELECT•INSERT•REPLACE•UPDATE•DELETE•EXPLAIN•SET•DECLARE•CASE•IF•RETURN•CALL OPTIMIZER_TRACE相关参数 TIPS参考 https://dev.mysql.com/doc/internals/en/system-variables-controlling-trace.html[1] • optimizer_trace
Applications should be prepared to handle the very rare case that a hashing function produces the same value for two different input values. One way to make collisions detectable is to make the hash column a primary key. Note Exploits for the MD5 and SHA-1 algorithms have become known. You...
迅速地;高速;急速地;急促;】. To the extent that the optimizer can use information about conditions on rows selected from one table and passed to the next, the more accurately【ˈækjərətli准确地;准确地,精确;正确,正确地;】 it can compute row estimates and choose the best execution...
setup_range_conditions tree = get_mm_tree(¶m, cond); 2. Fix the selectivity for SEL_ARGs by histogram fix_sel_tree_selectivity(¶m, tree); 3. Try to construct a QUICK_GROUP_MIN_MAX_SELECT group_trp = get_best_group_min_max(¶m, tree, &best_cost); 4. Try to construn...