Αποτελέσματα Αναζήτησης
6 Οκτ 2012 · I am trying to update a LARGE MyISAM table (25 million records) using a CLI script. The table is not being locked/used by anything else. I figured instead of doing single UPDATE queries for each record, I might as well utilize the CASE feature. The id field is PRIMARY.
6 Ιουν 2017 · The CASE expression can also be used in an UPDATE statement. You are familiar with the UPDATE statement; it changes or updates existing column values. If you want to update records based on column values, you can do it with the CASE expression.
MySQL CASE expression is a control flow structure that allows you to add if-else logic to a query. Generally speaking, you can use the CASE expression anywhere that allows a valid expression e.g., SELECT, WHERE and ORDER BY clauses. The CASE expression has two forms: simple CASE and searched CASE.
An UPDATE statement can start with a WITH clause to define common table expressions accessible within the UPDATE. See Section 15.2.20, “WITH (Common Table Expressions)”. Single-table syntax: UPDATE [LOW_PRIORITY] [IGNORE] table_reference . SET assignment_list . [WHERE where_condition] [ORDER BY ...] [LIMIT row_count] value: {expr | DEFAULT}
The MySQL UPDATE Statement. The UPDATE statement is used to modify the existing records in a table. UPDATE Syntax. UPDATE table_name. SET column1 = value1, column2 = value2, ... WHERE condition; Note: Be careful when updating records in a table! Notice the . WHERE clause in the UPDATE statement.
Definition and Usage. The CASE statement goes through conditions and return a value when the first condition is met (like an IF-THEN-ELSE statement). So, once a condition is true, it will stop reading and return the result. If no conditions are true, it will return the value in the ELSE clause.
23 Ιουν 2013 · UPDATE relation SET name1 = CASE WHEN userid1 = 3 THEN 'jack' ELSE name1 END, name2 = CASE WHEN userid2 = 3 THEN 'jack' ELSE name2 END WHERE (userid1 = 3 AND userid2 = 4) OR (userid1 = 4 AND userid2 = 3);
