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After the server accepts a connection, it enters Stage 2 of access control. For each request that you issue through the connection, the server determines what operation you want to perform, then checks whether your privileges are sufficient. This is where the privilege columns in the grant tables come into play. These privileges can come from any of theuser,global_grants,db,tables_priv,columns_priv, orprocs_priv tables. (You may find it helpful to refer toSection 8.2.3, “Grant Tables”, which lists the columns present in each grant table.)

Theuser andglobal_grants tables grant global privileges. The rows in these tables for a given account indicate the account privileges that apply on a global basis no matter what the default database is. For example, if theuser table grants you theDELETE privilege, you can delete rows from any table in any database on the server host. It is wise to grant privileges in theuser table only to people who need them, such as database administrators. For other users, leave all privileges in theuser table set to'N' and grant privileges at more specific levels only (for particular databases, tables, columns, or routines). It is also possible to grant database privileges globally but use partial revokes to restrict them from being exercised on specific databases (seeSection 8.2.12, “Privilege Restriction Using Partial Revokes”).

Thedb table grants database-specific privileges. Values in the scope columns of this table can take the following forms:

The server reads thedb table into memory and sorts it at the same time that it reads theuser table. The server sorts thedb table based on theHost,Db, andUser scope columns. As with theuser table, sorting puts the most-specific values first and least-specific values last, and when the server looks for matching rows, it uses the first match that it finds.

Thetables_priv,columns_priv, andprocs_priv tables grant table-specific, column-specific, and routine-specific privileges. Values in the scope columns of these tables can take the following forms:

The server sorts thetables_priv,columns_priv, andprocs_priv tables based on theHost,Db, andUser columns. This is similar todb table sorting, but simpler because only theHost column can contain wildcards.

The server uses the sorted tables to verify each request that it receives. For requests that require administrative privileges such asSHUTDOWN orRELOAD, the server checks only theuser andglobal_privilege tables because those are the only tables that specify administrative privileges. The server grants access if a row for the account in those tables permits the requested operation and denies access otherwise. For example, if you want to executemysqladmin shutdown but youruser table row does not grant theSHUTDOWN privilege to you, the server denies access without even checking thedb table. (The latter table contains noShutdown_priv column, so there is no need to check it.)

For database-related requests (INSERT,UPDATE, and so on), the server first checks the user's global privileges in theuser table row (less any privilege restrictions imposed by partial revokes). If the row permits the requested operation, access is granted. If the global privileges in theuser table are insufficient, the server determines the user's database-specific privileges from thedb table:

After determining the database-specific privileges granted by thedb table rows, the server adds them to the global privileges granted by theuser table. If the result permits the requested operation, access is granted. Otherwise, the server successively checks the user's table and column privileges in thetables_priv andcolumns_priv tables, adds those to the user's privileges, and permits or denies access based on the result. For stored-routine operations, the server uses theprocs_priv table rather thantables_priv andcolumns_priv.

Expressed in boolean terms, the preceding description of how a user's privileges are calculated may be summarized like this:

global privilegesOR database privilegesOR table privilegesOR column privilegesOR routine privileges

It may not be apparent why, if the global privileges are initially found to be insufficient for the requested operation, the server adds those privileges to the database, table, and column privileges later. The reason is that a request might require more than one type of privilege. For example, if you execute anINSERT INTO ... SELECT statement, you need both theINSERT and theSELECT privileges. Your privileges might be such that theuser table row grants one privilege global and thedb table row grants the other specifically for the relevant database. In this case, you have the necessary privileges to perform the request, but the server cannot tell that from either your global or database privileges alone. It must make an access-control decision based on the combined privileges.