SQLite C API provides a set of metadata interfaces (metadata available via SQL queries is beyond the scope of this section) with information dispersed over several pages (meta1, meta2, meta3, meta4, and meta5). Importantly, all these interfaces provide information about a single column in a prepared statement (with one exception noted below). There are three sources of metadata (16-bit UTF versions not shown):

• CREATE TABLE DDL statement (table source):
  • sqlite3_table_column_metadata
  • sqlite3_column_database_name
  • sqlite3_column_table_name
  • sqlite3_column_origin_name
  • sqlite3_column_decltype
• SQL statement (query source):
  • sqlite3_column_count
  • sqlite3_column_name
• particular table value (value source):
  • sqlite3_column_type

Table interfaces do not provide meaningful information on generated columns, possibly returning error codes or null pointers (see the official documentation for further details). The sqlite3_column_name interface returns the column alias from the query. When no alias is specified, the returned value is unspecified. The sqlite3_column_type interface returns type information about a particular row value, which is only meaningful if the database cursor points at a valid row.

SQLite C API supports retrieval of a single value only, i.e., a value in a particular column from the row pointed to by the database cursor (disregarding legacy interfaces). Furthermore, SQLite provides a set of type-specific column_* interfaces for this purpose. The caller is responsible for selecting a particular interface, with suitable selection reducing the chances of undesirable silent automatic typecasting.

SQLite employs dynamic typing. Each column has the so-called Affinity type determined based on the declared column type defined in the CREATE DDL statement. Affinity is the preferred column type, meaning that the column may store values of all SQLite supported types regardless of its affinity type. Type affinity is not available for generated columns, and for columns coming from a table, the sqlite3_column_decltype interface returns column DDL type definition as a string. TypeAffinityFromDeclaredType() converts this string to type affinity following the algorithm from the official SQLite documentation, and the AffinityMap attribute facilitates mapping affinity type to SQLite data type. Even for columns storing only values of a single data type matching the column affinity, it is still necessary to check the data type of individual for possible NULL.

ColumnMetaAPI() is the main method of the SQLiteCMeta class, retrieving all available metadata. TableMetaCollect(), in turn, wraps ColumnMetaAPI() and loops through columns. It also presets the ColumnIndex value in the metadata structure passed ByRef to ColumnMetaAPI(). The Initialized attribute is a flag used to confirm that the caller has set the ColumnIndex attribute. The MetaLoaded attribute of the SQLiteCExecSQL class is also a flag indicating that metadata is available.