Parse sqlite_schema

[kawasin73]

sqlite_schema is used to know table information.

[kawasin73]

• sqlite3_prepare_v2()
• sqlite3LockAndPrepare()
• sqlite3Prepare()
  • sqlite3BtreeSchemaLocked() for all databases
  • sqlite3RunParser()
• sqlite3RunParser()
  • get token one by one from sqlite3GetToken()
  • sqlite3Parser()
  • There is no implementation of sqlite3Parser()?
  • (sqlite3_stmt *) == (Vdbe *)

/*
** The interface to the LEMON-generated parser
*/
#ifndef SQLITE_AMALGAMATION
  void *sqlite3ParserAlloc(void*(*)(u64), Parse*);
  void sqlite3ParserFree(void*, void(*)(void*));
#endif
void sqlite3Parser(void*, int, Token);
int sqlite3ParserFallback(int);
#ifdef YYTRACKMAXSTACKDEPTH
  int sqlite3ParserStackPeak(void*);
#endif

https://www.sqlite.org/lemon.html

[kawasin73]

• sqlite3LocateTable() calls sqlite3ReadSchema()
• sqlite3Init() loads when DB_SchemaLoaded is not set
• int sqlite3InitOne()

/*
** Attempt to read the database schema and initialize internal
** data structures for a single database file.  The index of the
** database file is given by iDb.  iDb==0 is used for the main
** database.  iDb==1 should never be used.  iDb>=2 is used for
** auxiliary databases.  Return one of the SQLITE_ error codes to
** indicate success or failure.
*/
int sqlite3InitOne(sqlite3 *db, int iDb, char **pzErrMsg, u32 mFlags){

  /* Construct the in-memory representation schema tables (sqlite_schema or
  ** sqlite_temp_schema) by invoking the parser directly.  The appropriate
  ** table name will be inserted automatically by the parser so we can just
  ** use the abbreviation "x" here.  The parser will also automatically tag
  ** the schema table as read-only. */
  azArg[0] = "table";
  azArg[1] = zSchemaTabName = SCHEMA_TABLE(iDb);
  azArg[2] = azArg[1];
  azArg[3] = "1";
  azArg[4] = "CREATE TABLE x(type text,name text,tbl_name text,"
                            "rootpage int,sql text)";
  azArg[5] = 0;

  sqlite3InitCallback(&initData, 5, (char **)azArg, 0);

    zSql = sqlite3MPrintf(db, 
        "SELECT*FROM\"%w\".%s ORDER BY rowid",
        db->aDb[iDb].zDbSName, zSchemaTabName);

      rc = sqlite3_exec(db, zSql, sqlite3InitCallback, &initData, 0);

/*
** This is the callback routine for the code that initializes the
** database.  See sqlite3Init() below for additional information.
** This routine is also called from the OP_ParseSchema opcode of the VDBE.
**
** Each callback contains the following information:
**
**     argv[0] = type of object: "table", "index", "trigger", or "view".
**     argv[1] = name of thing being created
**     argv[2] = associated table if an index or trigger
**     argv[3] = root page number for table or index. 0 for trigger or view.
**     argv[4] = SQL text for the CREATE statement.
**
*/
int sqlite3InitCallback(void *pInit, int argc, char **argv, char **NotUsed){

    /* Call the parser to process a CREATE TABLE, INDEX or VIEW.
    ** But because db->init.busy is set to 1, no VDBE code is generated
    ** or executed.  All the parser does is build the internal data
    ** structures that describe the table, index, or view.
    **
    ** No other valid SQL statement, other than the variable CREATE statements,
    ** can begin with the letters "C" and "R".  Thus, it is not possible run
    ** any other kind of statement while parsing the schema, even a corrupt
    ** schema.
    */

    if( sqlite3GetUInt32(argv[3], &db->init.newTnum)==0
     || (db->init.newTnum>pData->mxPage && pData->mxPage>0)
    ){

    TESTONLY(rcp = ) sqlite3Prepare(db, argv[4], -1, 0, 0, &pStmt, 0);

The parser calls sqlite3StartTable() for CREATE TABLE statement.

/*
** This routine is called to report the final ")" that terminates
** a CREATE TABLE statement.
**
** The table structure that other action routines have been building
** is added to the internal hash tables, assuming no errors have
** occurred.
**
** An entry for the table is made in the schema table on disk, unless
** this is a temporary table or db->init.busy==1.  When db->init.busy==1
** it means we are reading the sqlite_schema table because we just
** connected to the database or because the sqlite_schema table has
** recently changed, so the entry for this table already exists in
** the sqlite_schema table.  We do not want to create it again.
**
** If the pSelect argument is not NULL, it means that this routine
** was called to create a table generated from a 
** "CREATE TABLE ... AS SELECT ..." statement.  The column names of
** the new table will match the result set of the SELECT.
*/
void sqlite3EndTable(

  /* If the db->init.busy is 1 it means we are reading the SQL off the
  ** "sqlite_schema" or "sqlite_temp_schema" table on the disk.
  ** So do not write to the disk again.  Extract the root page number
  ** for the table from the db->init.newTnum field.  (The page number
  ** should have been put there by the sqliteOpenCb routine.)
  **
  ** If the root page number is 1, that means this is the sqlite_schema
  ** table itself.  So mark it read-only.
  */
  if( db->init.busy ){
    if( pSelect || (!IsOrdinaryTable(p) && db->init.newTnum) ){
      sqlite3ErrorMsg(pParse, "");
      return;
    }
    p->tnum = db->init.newTnum;
    if( p->tnum==1 ) p->tabFlags |= TF_Readonly;
  }

  /* Add the table to the in-memory representation of the database.
  */

    pOld = sqlite3HashInsert(&pSchema->tblHash, p->zName, p);

• parsed table info is stored in Parse.pNewTable. p in sqlite3EndTable() is Parse.pNewTable.

void sqlite3StartTable(

zName = sqlite3NameFromToken(db, pName);

pTable->zName = zName;

pParse->pNewTable = pTable;

char *sqlite3NameFromToken(sqlite3 *db, const Token *pName){
  char *zName;
  if( pName ){
    zName = sqlite3DbStrNDup(db, (const char*)pName->z, pName->n);
    sqlite3Dequote(zName);

• the table's name is the same as the create table statement. not lower cased?
• The hash function of hash map converts upper/lower case.

/*
** The hashing function.
*/
static unsigned int strHash(const char *z){
  unsigned int h = 0;
  unsigned char c;
  while( (c = (unsigned char)*z++)!=0 ){     /*OPTIMIZATION-IF-TRUE*/
    /* Knuth multiplicative hashing.  (Sorting & Searching, p. 510).
    ** 0x9e3779b1 is 2654435761 which is the closest prime number to
    ** (2**32)*golden_ratio, where golden_ratio = (sqrt(5) - 1)/2. */
    h += sqlite3UpperToLower[c];
    h *= 0x9e3779b1;
  }
  return h;
}