![Alter Alter](/uploads/1/2/5/5/125513297/873122059.png)
Summary: in this tutorial, we will show you how to use the PostgreSQL ADD COLUMN statement to add one or more columns to an existing database table. Introduction to the PostgreSQL ADD COLUMN statement. To add a new column to an existing table, you use the ALTER TABLE ADD COLUMN statement as follows. Note: Before MariaDB 10.2.1, constraint expressions were accepted in syntax, but ignored. ALTER TABLE tablename ADD CONSTRAINT constraintname CHECK(expression); Before a row is inserted or updated, all constraints are evaluated in the order they are defined.
ADD COLUMN columnname columndefinition FIRST AFTER existingcolumn;Let’s examine the statement in more detail. First, you specify the table name after the ALTER TABLE clause. Second, you put the new column and its definition after the ADD COLUMN clause. Note that COLUMN keyword is optional so you can omit it. Third, MySQL allows you to add the new column as the first column of the table by specifying the FIRST keyword. It also allows you to add the new column after an existing column using the AFTER existingcolumn clause.
If you don’t explicitly specify the position of the new column, MySQL will add it as the last column.To add two or more columns to a table at the same time, you use the following syntax. Error Code: 1060. Duplicate column name 'vendorgroup'For the table with a few columns, it is easy to see which columns are already there. However, with a big table with hundred of columns, it is more difficult.In some situations, you want to check whether a column already exists in a table before adding it. However, there is no statement like ADD COLUMN IF NOT EXISTS available. Fortunately, you can get this information from the columns table of the informationschema database as the following query.
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