描述
要执行SQL查询，必须首先使用其中一个准备函数将其编译成字节码程序。
C / C ++语法
int sqlite3_prepare_v2( sqlite3 *db, const char *zSql, int nByte, sqlite3_stmt **ppStmt, const char **pzTail ); |
PB语法
FUNCTION sqlite3_prepare_v2 ( _ BYVAL hDbc AS DWORD, _ BYREF szSql AS ASCIIZ, _ BYVAL nBytes AS LONG, _ BYREF ppStmt AS DWORD, _ BYREF pszTail AS DWORD _ ) AS LONG |
参数
pDb
[in]数据库连接句柄。必须是从sqlite3_open，sqlite3_open16或sqlite3_open_v2获取的sqlite3对象指针。 数据库连接不能关闭。
szSql
[in]要编译的语句，编码为UTF-8。
nBytes
[in]如果为nbytes参数小于零，则szSql读取到第一个零终止符。如果为nbytes为非负数，则为从szSql读取的最大字节数。当为nbytes为非负数时，szSql字符串以第一个“\\ 000”或“\\ u0000”字符或第nB字节结尾，以先到者为准。如果调用者知道提供的字符串是非终止的，那么通过传递等于输入字符串中包含Nul-Terminator字节的字节数的为nbytes参数可以获得较小的性能优势，因为这样保存SQLite不必制作输入字符串的副本。
ppStmt
[inout]ppStmt指向可以使用sqlite3_step执行的编译准备语句。如果有错误，ppStmt设置为NULL。如果输入文本不包含SQL（如果输入是空字符串或注释），则ppStmt设置为NULL。调用过程完成后，负责使用sqlite3_finalize删除编译的SQL语句。ppStmt可能不为空。
pszTail
[in]如果pzTail不为NULL，则指向szSql中第一个SQL语句结尾的第一个字节。这些函数仅在szSql中编译第一个语句，因此pzTail指向未编译的内容。
返回值
如果成功返回SQLITE_OK，否则返回错误代码。
C ++实现代码
/*
** Compile the UTF-8 encoded SQL statement zSql into a statement handle.
*/
static int sqlite3Prepare(
sqlite3 *db, /* Database handle. */
const char *zSql, /* UTF-8 encoded SQL statement. */
int nBytes, /* Length of zSql in bytes. */
int saveSqlFlag, /* True to copy SQL text into the sqlite3_stmt */
Vdbe *pReprepare, /* VM being reprepared */
sqlite3_stmt **ppStmt, /* OUT: A pointer to the prepared statement */
const char **pzTail /* OUT: End of parsed string */
){
Parse *pParse; /* Parsing context */
char *zErrMsg = 0; /* Error message */
int rc = SQLITE_OK; /* Result code */
int i; /* Loop counter */
/* Allocate the parsing context */
pParse = sqlite3StackAllocZero(db, sizeof(*pParse));
if( pParse==0 ){
rc = SQLITE_NOMEM;
goto end_prepare;
}
pParse->pReprepare = pReprepare;
assert( ppStmt && *ppStmt==0 );
assert( !db->mallocFailed );
assert( sqlite3_mutex_held(db->mutex) );
/* Check to verify that it is possible to get a read lock on all
** database schemas. The inability to get a read lock indicates that
** some other database connection is holding a write-lock, which in
** turn means that the other connection has made uncommitted changes
** to the schema.
**
** Were we to proceed and prepare the statement against the uncommitted
** schema changes and if those schema changes are subsequently rolled
** back and different changes are made in their place, then when this
** prepared statement goes to run the schema cookie would fail to detect
** the schema change. Disaster would follow.
**
** This thread is currently holding mutexes on all Btrees (because
** of the sqlite3BtreeEnterAll() in sqlite3LockAndPrepare()) so it
** is not possible for another thread to start a new schema change
** while this function is running. Hence, we do not need to hold
** locks on the schema, we just need to make sure nobody else is
** holding them.
**
** Note that setting READ_UNCOMMITTED overrides most lock detection,
** but it does *not* override schema lock detection, so this all still
** works even if READ_UNCOMMITTED is set.
*/
for(i=0; i<db->nDb; i++) {
Btree *pBt = db->aDb[i].pBt;
if( pBt ){
assert( sqlite3BtreeHoldsMutex(pBt) );
rc = sqlite3BtreeSchemaLocked(pBt);
if( rc ){
const char *zDb = db->aDb[i].zName;
sqlite3Error(db, rc, "database schema is locked: %s", zDb);
testcase( db->flags & SQLITE_ReadUncommitted );
goto end_prepare;
}
}
}
sqlite3VtabUnlockList(db);
pParse->db = db;
pParse->nQueryLoop = (double)1;
if( nBytes>=0 && (nBytes==0 || zSql[nBytes-1]!=0) ){
char *zSqlCopy;
int mxLen = db->aLimit[SQLITE_LIMIT_SQL_LENGTH];
testcase( nBytes==mxLen );
testcase( nBytes==mxLen+1 );
if( nBytes>mxLen ){
sqlite3Error(db, SQLITE_TOOBIG, "statement too long");
rc = sqlite3ApiExit(db, SQLITE_TOOBIG);
goto end_prepare;
}
zSqlCopy = sqlite3DbStrNDup(db, zSql, nBytes);
if( zSqlCopy ){
sqlite3RunParser(pParse, zSqlCopy, &zErrMsg);
sqlite3DbFree(db, zSqlCopy);
pParse->zTail = &zSql[pParse->zTail-zSqlCopy];
}else{
pParse->zTail = &zSql[nBytes];
}
}else{
sqlite3RunParser(pParse, zSql, &zErrMsg);
}
assert( 1==(int)pParse->nQueryLoop );
if( db->mallocFailed ){
pParse->rc = SQLITE_NOMEM;
}
if( pParse->rc==SQLITE_DONE ) pParse->rc = SQLITE_OK;
if( pParse->checkSchema ){
schemaIsValid(pParse);
}
if( db->mallocFailed ){
pParse->rc = SQLITE_NOMEM;
}
if( pzTail ){
*pzTail = pParse->zTail;
}
rc = pParse->rc;
#ifndef SQLITE_OMIT_EXPLAIN
if( rc==SQLITE_OK && pParse->pVdbe && pParse->explain ){
static const char * const azColName[] = {
"addr", "opcode", "p1", "p2", "p3", "p4", "p5", "comment",
"selectid", "order", "from", "detail"
};
int iFirst, mx;
if( pParse->explain==2 ){
sqlite3VdbeSetNumCols(pParse->pVdbe, 4);
iFirst = 8;
mx = 12;
}else{
sqlite3VdbeSetNumCols(pParse->pVdbe, 8);
iFirst = 0;
mx = 8;
}
for(i=iFirst; i<mx; i++){
sqlite3VdbeSetColName(pParse->pVdbe, i-iFirst, COLNAME_NAME,
azColName[i], SQLITE_STATIC);
}
}
#endif
assert( db->init.busy==0 || saveSqlFlag==0 );
if( db->init.busy==0 ){
Vdbe *pVdbe = pParse->pVdbe;
sqlite3VdbeSetSql(pVdbe, zSql, (int)(pParse->zTail-zSql), saveSqlFlag);
}
if( pParse->pVdbe && (rc!=SQLITE_OK || db->mallocFailed) ){
sqlite3VdbeFinalize(pParse->pVdbe);
assert(!(*ppStmt));
}else{
*ppStmt = (sqlite3_stmt*)pParse->pVdbe;
}
if( zErrMsg ){
sqlite3Error(db, rc, "%s", zErrMsg);
sqlite3DbFree(db, zErrMsg);
}else{
sqlite3Error(db, rc, 0);
}
/* Delete any TriggerPrg structures allocated while parsing this statement. */
while( pParse->pTriggerPrg ){
TriggerPrg *pT = pParse->pTriggerPrg;
pParse->pTriggerPrg = pT->pNext;
sqlite3DbFree(db, pT);
}
end_prepare:
sqlite3StackFree(db, pParse);
rc = sqlite3ApiExit(db, rc);
assert( (rc&db->errMask)==rc );
return rc;
}
static int sqlite3LockAndPrepare(
sqlite3 *db, /* Database handle. */
const char *zSql, /* UTF-8 encoded SQL statement. */
int nBytes, /* Length of zSql in bytes. */
int saveSqlFlag, /* True to copy SQL text into the sqlite3_stmt */
Vdbe *pOld, /* VM being reprepared */
sqlite3_stmt **ppStmt, /* OUT: A pointer to the prepared statement */
const char **pzTail /* OUT: End of parsed string */
){
int rc;
assert( ppStmt!=0 );
*ppStmt = 0;
if( !sqlite3SafetyCheckOk(db) ){
return SQLITE_MISUSE_BKPT;
}
sqlite3_mutex_enter(db->mutex);
sqlite3BtreeEnterAll(db);
rc = sqlite3Prepare(db, zSql, nBytes, saveSqlFlag, pOld, ppStmt, pzTail);
if( rc==SQLITE_SCHEMA ){
sqlite3_finalize(*ppStmt);
rc = sqlite3Prepare(db, zSql, nBytes, saveSqlFlag, pOld, ppStmt, pzTail);
}
sqlite3BtreeLeaveAll(db);
sqlite3_mutex_leave(db->mutex);
assert( rc==SQLITE_OK || *ppStmt==0 );
return rc;
}
/*
** Two versions of the official API. Legacy and new use. In the legacy
** version, the original SQL text is not saved in the prepared statement
** and so if a schema change occurs, SQLITE_SCHEMA is returned by
** sqlite3_step(). In the new version, the original SQL text is retained
** and the statement is automatically recompiled if an schema change
** occurs.
*/
SQLITE_API int sqlite3_prepare(
sqlite3 *db, /* Database handle. */
const char *zSql, /* UTF-8 encoded SQL statement. */
int nBytes, /* Length of zSql in bytes. */
sqlite3_stmt **ppStmt, /* OUT: A pointer to the prepared statement */
const char **pzTail /* OUT: End of parsed string */
){
int rc;
rc = sqlite3LockAndPrepare(db,zSql,nBytes,0,0,ppStmt,pzTail);
assert( rc==SQLITE_OK || ppStmt==0 || *ppStmt==0 ); /* VERIFY: F13021 */
return rc;
}
SQLITE_API int sqlite3_prepare_v2(
sqlite3 *db, /* Database handle. */
const char *zSql, /* UTF-8 encoded SQL statement. */
int nBytes, /* Length of zSql in bytes. */
sqlite3_stmt **ppStmt, /* OUT: A pointer to the prepared statement */
const char **pzTail /* OUT: End of parsed string */
){
int rc;
rc = sqlite3LockAndPrepare(db,zSql,nBytes,1,0,ppStmt,pzTail);
assert( rc==SQLITE_OK || ppStmt==0 || *ppStmt==0 ); /* VERIFY: F13021 */
return rc;
}