What happens to data when you alter the table structure?

Question

Existing tables can be altered with an ALTER TABLE statement. An ALTER TABLE statement is part of DDL, and is for altering a table schema only; we'll look at .

What happens when you ALTER a table structure?

It is important to consider how schema changes will affect the data in a table. Adding an extra column to a table will add an extra column to all existing rows, just as it would in a spreadsheet. Deleting a column means all data in that column will be lost forever.

Does ALTER TABLE change data?

The basic syntax of an ALTER TABLE command to change the DATA TYPE of a column in a table is as follows. ALTER TABLE table_name MODIFY COLUMN column_name datatype; The basic syntax of an ALTER TABLE command to add a NOT NULL constraint to a column in a table is as follows.

Does ALTER TABLE remove data?

No it will not erase your data. It will add a column and all the existing data will be assigned null values in this column.

What deals with creating altering a table structure in the database?

1. Data Definition Language (DDL) DDL changes the structure of the table like creating a table, deleting a table, altering a table, etc.

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