The context can be any kind of value and will be passed to wrapIdentifier without modification. SERIAL asks to create UNIQUE index, PK asks to create PRIMARY index - so 2 indices are created. MySQL always creates an index when you ask for this. quer圜ontext #Īllows configuring a context to be passed to the wrapIdentifier hook for formatting table builder identifiers. More correct 'columns mentioned in PK expression' - PK may be built by any valid expression and not refer to column separately and directly. Defaults to tablename_pkey unless constraintName is specified. For example, to drop multiple columns in a single statement, do this: Press CTRL+C to copy. dropPrimary #ĭrops the primary key constraint on a table. This is a MySQL extension to standard SQL, which permits only one of each clause per ALTER TABLE statement. MySQL / MariaDB- Specific Index Options - MySQL-specific options available. , I could make more than one index on the same column. ADD INDEX col (col) statement, see the accepted answer and the comment under the one that uses only ADD INDEX (col). A default unique key name using the columns is used unless indexName is specified (in which case columns is ignored). For a no-frills, single column constraint, adding uniqueTrue to the Column. To avoid duplicate indexes on the same columns, do not use this or ALTER. In addition, unique constraints are defined as part of ANSI standard, while indexes are not. MySQL UNIQUE constraint syntax is ANSI SQL compatible. dropUnique #ĭrops a unique key constraint from a table. One of the major differences between a unique constraint and a unique index is that a foreign key constraint on another table can reference columns that make up a unique constraint. Ensures that a value in a column, or a group of columns, is unique across the entire table. A default foreign key name using the columns is used unless foreignKeyName is specified (in which case columns is ignored). Table.dropForeign(columns, )ĭrops a foreign key constraint from a table. MySQL ALTER TABLE ADD and DROP column, INDEX, PRIMARY KEY and FOREIGN KEY. Table.increments(name, options= ) dropForeign # If you want to add a UNIQUE INDEX named cateid on cateid column for the table newbookmast, the following statement can be used. Renames a column from one name to another. dropSchemaIfExists ( 'public', true ) Schema Building # dropColumn #ĭrops a column, specified by the column's name dropColumns #ĭrops multiple columns, taking a variable number of column names. dropSchemaIfExists ( 'public' ) //drop schema if exists 'public' cascade Run the above code line in any browser compatible with MySQL.Knex. You may modify an existing table by similarly adding a new unique constraint. We will use the keyword UNIQUE to make the combination of email and department a unique column. An error will be generated if you insert or change a value that duplicates data in the email+department column. Like the first, we created an EmployeeDepartment table containing the variables email and department. We will designate an email as a unique column using the keyword UNIQUE. If you change or edit a value that duplicates data in the email column, an error will be generated. In the first example that came before, we created a database called Employees with the attributes email, first_Name, and last_Name. We create a column with unique value called supplierID. CREATE TABLE Employees( email varchar( 255) UNIQUE, first_Name VARCHAR( 255), last_Name VARCHAR( 255) ) CREATE TABLE EmployeeDepartment( email varchar( 255), department varchar( 255), UNIQUE(email,department) ) - If the Employees table does not have a unique email constraintĪLTER TABLE EmployeeDepartment ADD UNIQUE email - If the EmployeeDepartment table does not have a unique constraintĪLTER TABLE EmployeeDepartment ADD UNIQUE `unique_department_emp `(email,department) We could create a table called suppliers to store suppliers data (e.g., name, address and phone number).
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