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9 maj 2013 · DELETE FROM table WHERE unique_key=x; DELETE FROM table WHERE unique_key=y; INSERT INTO table VALUES (unique_key=y, field=record1), (unique_key=x, field=record2); Alter my primary/unique key and then substitute them with the modified value: UPDATE table SET unique_key=x* WHERE unique_key=x;
21 maj 2012 · Method 3: Populate using an UPDATE statement. This case would occur when, for example, there was a value from another part of your application that needs to be added to the table, or you need to specify an exact order for the unique values. BEGIN TRANSACTION ALTER TABLE MyTable ADD MyColumn int NULL UPDATE MyTable SET MyColumn = ...
26 sty 2024 · Using ON DUPLICATE KEY UPDATE. VALUES ('jane.doe@example.com', 'janedoe') ON DUPLICATE KEY UPDATE username = VALUES (username); ‘ON DUPLICATE KEY UPDATE’ allows you to update certain values when a UNIQUE constraint is triggered, ensuring data stays fresh without errors.
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}
16 kwi 2016 · UPDATE Tests AS old INNER JOIN ( SELECT 10 AS TestId, 25 AS TestSubId, 1000 AS TestScore, 2000 AS TestScore2 UNION ALL SELECT 11, 22, 1100, 2100 ) AS new ON old.TestId = new.TestId AND old.TestSubId = new.TestSubId SET old.TestScore = new.TestScore, old.TestScore2 = new.TestScore2 ;
MySQL UNIQUE Constraint. The UNIQUE constraint ensures that all values in a column are different. Both the UNIQUE and PRIMARY KEY constraints provide a guarantee for uniqueness for a column or set of columns. A PRIMARY KEY constraint automatically has a UNIQUE constraint.
If you insert or update a value that causes a duplicate in the column1, MySQL rejects the change and issues an error. This UNIQUE constraint is a column constraint. And you can use it to enforce the unique rule for one column.
