The Schema Table

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The Schema Table

# 1. Introduction

Every SQLite database contains a single "schema table" that stores the schema for that database. The schema for a database is a description of all of the other tables, indexes, triggers, and views that are contained within the database. The schema table looks like this:

>     CREATE TABLE sqlite_schema(
>       type text,
>       name text,
>       tbl_name text,
>       rootpage integer,
>       sql text
>     );

The sqlite_schema table contains one row for each table, index, view, and trigger (collectively "objects") in the schema, except there is no entry for the sqlite_schema table itself. See the schema storage subsection of the file format documentation for additional information on how SQLite uses the sqlite_schema table internally.

# 2. Alternative Names

The schema table can always be referenced using the name "sqlite_schema", especially if qualifed by the schema name like "main.sqlite_schema" or "temp.sqlite_schema". But for historical compatibility, some alternative names are also recognized, including:

1. sqlite_master
2. sqlite_temp_schema
3. sqlite_temp_master

Alternatives (2) and (3) only work for the TEMP database associated with each database connection, but alternative (1) works anywhere. For historical reasons, callbacks from the sqlite3_set_authorizer() interface always refer to the schema table using names (1) or (3).

# 3. Interpretation Of The Schema Table

The meanings of the fields of the schema table are as follows:

type

  The sqlite_schema.type column will be one of the following text strings: 'table', 'index', 'view', or 'trigger' according to the type of object defined. The 'table' string is used for both ordinary and virtual tables.

name

  The sqlite_schema.name column will hold the name of the object. (UNIQUE and PRIMARY KEY constraints on tables cause SQLite to create internal indexes with names of the form "sqlite_autoindex_TABLE_N" where TABLE is replaced by the name of the table that contains the constraint and N is an integer beginning with 1 and increasing by one with each constraint seen in the table definition. In a WITHOUT ROWID table, there is no sqlite_schema entry for the PRIMARY KEY, but the "sqlite_autoindex_TABLE_N" name is set aside for the PRIMARY KEY as if the sqlite_schema entry did exist. This will affect the numbering of subsequent UNIQUE constraints. The "sqlite_autoindex_TABLE_N" name is never allocated for an INTEGER PRIMARY KEY, either in rowid tables or WITHOUT ROWID tables.

tbl_name

  The sqlite_schema.tbl_name column holds the name of a table or view that the object is associated with. For a table or view, the tbl_name column is a copy of the name column. For an index, the tbl_name is the name of the table that is indexed. For a trigger, the tbl_name column stores the name of the table or view that causes the trigger to fire.

rootpage

  The sqlite_schema.rootpage column stores the page number of the root b-tree page for tables and indexes. For rows that define views, triggers, and virtual tables, the rootpage column is 0 or NULL.

sql

  The sqlite_schema.sql column stores SQL text that describes the object. This SQL text is a CREATE TABLE, CREATE VIRTUAL TABLE, CREATE INDEX, CREATE VIEW, or CREATE TRIGGER statement that if evaluated against the database file when it is the main database of a database connection would recreate the object. The text is usually a copy of the original statement used to create the object but with normalizations applied so that the text conforms to the following rules:

  - The CREATE, TABLE, VIEW, TRIGGER, and INDEX keywords at the beginning of the statement are converted to all upper case letters.
  - The TEMP or TEMPORARY keyword is removed if it occurs after the initial CREATE keyword.
  - Any database name qualifier that occurs prior to the name of the object being created is removed.
  - Leading spaces are removed.
  - All spaces following the first two keywords are converted into a single space.

  The text in the sqlite_schema.sql column is a copy of the original CREATE statement text that created the object, except normalized as described above and as modified by subsequent ALTER TABLE statements. The sqlite_schema.sql is NULL for the internal indexes that are automatically created by UNIQUE or PRIMARY KEY constraints.