For knowing the structure of the table, we use DESC tablename. It will not show which column is the primary key....
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What is the command for knowing the complete structure of the table?
The recommended way to retrieve information about your database, tables or columns is to use the INFORMATION_SCHEMA views. These views were introduced in the SQL-92 standard, and all database vendors have adopted or will soon adopt this standard.
Retrieving information about primary keys may require joining a couple of these views. For example, the following query (posted here and found via a Web search for "information_schema primary key") will show the primary keys for each table --
SELECT T.TABLE_NAME, COALESCE( CU.CONSTRAINT_NAME , '(no primary key)') AS PRIMARY_KEY_NAME, CU.COLUMN_NAME FROM INFORMATION_SCHEMA.TABLES AS T LEFT JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS AS TC ON TC.TABLE_CATALOG = T.TABLE_CATALOG AND TC.TABLE_SCHEMA = T.TABLE_SCHEMA AND TC.TABLE_NAME = T.TABLE_NAME AND TC.CONSTRAINT_TYPE = 'PRIMARY KEY' LEFT JOIN INFORMATION_SCHEMA.KEY_COLUMN_USAGE AS CU ON CU.CONSTRAINT_CATALOG = TC.CONSTRAINT_CATALOG AND CU.CONSTRAINT_SCHEMA = TC.CONSTRAINT_SCHEMA AND CU.CONSTRAINT_NAME = TC.CONSTRAINT_NAME WHERE T.TABLE_TYPE = 'BASE TABLE' ORDER BY T.TABLE_NAME, CU.ORDINAL_POSITION
Note that this query works in Microsoft SQL Server but might need tweaking for whatever database system you're using.
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