What is "sql-table"

In relational database models, the table is a set of data arranged in number of columns and number of rows. For example, a table containing employee data for a company may contain a row for each employee and columns representing employee information such as employee number, name, address, position and home phone number.

Columns are typically considered to be the fields in the table, and characterize the types of data that should be in the table (numerical, alpha-numeric, dates, coordinates, etc.). The number of rows can be interpreted as the number of combinations of values of the table fields, and can contain identical rows depending on the goal. The way to unambiguously reference a single line is by using a primary key.

You can assign properties to the table and to each column in the table to control the data that is allowed and other properties. For example, you can create constraints in a column to disapprove null values or provide a default value if a value is not specified, or you can assign a key constraint in the table that imposes exclusivity or sets a relation between tables.

In addition to the data type inherent to all columns of a table, some may have associated constraints: uniqueness (SQL: UNIQUE), prohibition of values NULL (SQL: NOT NULL), value delimitation, etc. These restrictions prevent the insertion of unwanted values that compromise the validity and integrity of data.