SQL Tables Content.
What is a Database Table?
- Tables are the basic building blocks in any database.
- They hold the rows and columns of your data.
- You can create tables, change them, and remove them.
- Normally, a user who creates a table is owner of the table and is responsible for granting permission to use it. That means how to give permission to use what and how.
When you create a table with SQL, you do at least the following:
- Name of the table.
- Name of the columns it contains.
- Specify the data type of each column.
- Specify the null status of each column - whether that column permits or forbids null values.
Almost all vendors have accepted additional possibilities
for the CREATE TABLE statement which is supported in SQL-standard, including:
- Defaults (values assumed when you don't explicitly enter anything, such as today's date, on a sales order).
- Constraints that check (limit) the possible values you can enter for a column (for example, pub_ids can be 0736, 0877, or 1389 only).
- Constraints that defines a column as primary key, unique, or both.
- Constraints that defines index for columns to achieve fast search and data retrieval.
- Constraints that can set up reference checks among primary and foreign keys.
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