![]() Also notice that MySQL has added the constraint as a table constraint (i.e. This time it has /*!80016 NOT ENFORCED */ against the constraint definition. `ProductPrice` decimal(8,2) DEFAULT NULL,ĬONSTRAINT `ProductPrice_chk` CHECK ((`ProductPrice` > 0)) /*!80016 NOT ENFORCED */ Let’s check the table’s definition again: SHOW CREATE TABLE Products This time it tells us that the query was OK, and no error was returned. Result: Query OK, 0 rows affected (0.01 sec) Let’s now try to create the constraint again, but this time we’ll include NOT ENFORCED in its definition: ALTER TABLE ProductsĪDD CONSTRAINT ProductPrice_chk CHECK (ProductPrice > 0) NOT ENFORCED We can see that there are no CHECK constraints. ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci | Let’s use the SHOW CREATE TABLE statement to view the definition of our table: SHOW CREATE TABLE Products However, the CHECK constraint wasn’t even created. We get the same error that tells us that the CHECK constraint was violated. Now let’s try to add our (enforced) CHECK constraint: ALTER TABLE Products But because we haven’t yet added our CHECK constraint, the data was inserted without error. This data violates the CHECK constraint that we are about to try to add to our table. ![]() Result: Query OK, 1 row affected (0.00 sec) Now let’s add data before we add the CHECK constraint: INSERT INTO Products Let’s drop the table and create it again: DROP TABLE Products If we define it as NOT ENFORCED, then the constraint will be created and we won’t get an error.So if we don’t specify NOT ENFORCED, then it will be ENFORCED by default. Bear in mind that this is the default option. If we define the CHECK constraint as ENFORCED, then the constraint won’t be created and we’ll get an error.When we try to add a CHECK constraint to a table that already violates the CHECK constraint, the result will depend on whether we define the CHECK constraint as ENFORCED or NOT ENFORCED: When Existing Data Violates the CHECK Constraint That would have created a CHECK constraint that does the same thing, and MySQL would have automatically generated a name for it. We could have used the following code: ALTER TABLE Products We also explicitly used the CONSTRAINT keyword, although this is also optional. If we hadn’t provided a name, MySQL would have automatically generated a name for the constraint. When we added the constraint, we provided a name for it. Specifically, it’s because we’re trying to insert zero into the column, but our CHECK constraint specifies that the value has to be greater than zero. The error tells us that our CHECK constraint was violated. ![]() Result: ERROR 3819 (HY000): Check constraint 'ProductPrice_chk' is violated. Now if we try to insert zero into that column, we get an error: INSERT INTO Products Here, we added a constraint to check that any data entered into the ProductPrice column is greater than zero. Here’s an example of adding a constraint to that table: ALTER TABLE ProductsĪDD CONSTRAINT ProductPrice_chk CHECK (ProductPrice > 0) Suppose we create the following table: CREATE TABLE Products ( So our actual code could be as simple as this: ALTER TABLE The parts in square brackets are optional. The syntax for adding a CHECK constraint to an existing table goes like this: ALTER TABLE ĪDD ] CHECK (condition) ENFORCED] To add a CHECK constraint to an existing table, we can use the ALTER TABLE statement. We can create them at the time of creating the table, or we can add the constraint later. `Name ` FROM `IceCreams ` AS `i ` ORDER BY `i `.As of MySQL 8.0.16, we can create CHECK constraints in MySQL. INSERT INTO `IceCreams ` ( `IceCreamId `, `Name `) INSERT INTO `IceCreams ` ( `IceCreamId `, `AutoGeneratedUniqueId `, `Name `) `AutoGeneratedUniqueId ` int NOT NULL AUTO_INCREMENT,ĬONSTRAINT `PK_IceCreams ` PRIMARY KEY ( `IceCreamId `),ĬONSTRAINT `AK_IceCreams_AutoGeneratedUniqueId ` UNIQUE ( `AutoGeneratedUniqueId `)Įxecuted DbCommand (12ms), CommandType = 'Text ', CommandTimeout = '30 '] `Name ` longtext CHARACTER SET utf8mb4 NULL, CommandĮxecuted DbCommand (5ms), CommandType = 'Text ', CommandTimeout = '30 ']Įxecuted DbCommand (86ms), CommandType = 'Text ', CommandTimeout = '30 ']
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