每个 SQLite 数据库都包含一个“模式表”，用于存储该数据库的模式。数据库的模式是对数据库中包含的所有其他表、索引、触发器和视图的描述。架构表如下所示：
CREATE TABLE sqlite_schema( type text, name text, tbl_name text, rootpage integer, sql text );
备选方案 (2) 和 (3) 仅适用于与每个数据库连接关联的 TEMP 数据库，但备选方案 (1) 适用于任何地方。由于历史原因，来自sqlite3_set_authorizer() 接口的回调总是使用名称 (1) 或 (3) 引用模式表。
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.
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.
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.
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.
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.
SQLite 在创建数据库时创建模式表，并在 SQLite 用户提交 DDL 语句以供执行时修改其内容。用户一般情况下无需修改，修改后需承担数据库损坏的风险。