For example, a “unique” constraint specifies that no two records can have the same value in a particular column. A constraint is basically a rule associated with a column that the data entered into that column must follow. What are constraints? When tables are created, it is common for one or more columns to have constraints associated with them. Number value with a maximum number of digits of “size” total, with a maximum number of “d” digits to the right of the decimal. Number value with a max number of column digits specified in parenthesis. Here are the most common Data types: char(size)įixed-length character string. If a column called “Last_Name”, is to be used to hold names, then that particular column should have a “varchar” (variable-length character) data type. Do not use any SQL reserved keywords as names for tables or column names (such as “select”, “create”, “insert”, etc).ĭata types specify what the type of data can be for that particular column. The table and column names must start with a letter and can be followed by letters, numbers, or underscores – not to exceed a total of 30 characters in length. All SQL statements should end with a “ ”. Make sure you separate each column definition with a comma. It is important to make sure you use an open parenthesis before the beginning table, and a closing parenthesis after the end of the last column definition. To create a new table, enter the keywords create table followed by the table name, followed by an open parenthesis, followed by the first column name, followed by the data type for that column, followed by any optional constraints, and followed by a closing parenthesis. Note: You may have as many columns as you’d like, and the constraints are optional. Here is the format of a simple create table statement: create table "tablename"įormat of create table if you were to use optional constraints: create table "tablename" The create table statement is used to create a new table.
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