/*
** Return a list of all triggers on table pTab if there exists at least
** one trigger that must be fired when an operation of type 'op' is
** performed on the table, and, if that operation is an UPDATE, if at
** least one of the columns in pChanges is being modified.
*/
SQLITE_PRIVATE Trigger *sqlite3TriggersExist(
Parse *pParse, /* Parse context */
Table *pTab, /* The table the contains the triggers */
int op, /* one of TK_DELETE, TK_INSERT, TK_UPDATE */
ExprList *pChanges, /* Columns that change in an UPDATE statement */
int *pMask /* OUT: Mask of TRIGGER_BEFORE|TRIGGER_AFTER */
){
int mask = 0;
Trigger *pList = 0;
Trigger *p;
if( (pParse->db->flags & SQLITE_EnableTrigger)!=0 ){
pList = sqlite3TriggerList(pParse, pTab);
}
assert( pList==0 || IsVirtual(pTab)==0 );
for(p=pList; p; p=p->pNext){
if( p->op==op && checkColumnOverlap(p->pColumns, pChanges) ){
mask |= p->tr_tm;
}
}
if( pMask ){
*pMask = mask;
}
return (mask ? pList : 0);
}
/*
** Generate the text of a WHERE expression which can be used to select all
** temporary triggers on table pTab from the sqlite_temp_master table. If
** table pTab has no temporary triggers, or is itself stored in the
** temporary database, NULL is returned.
*/
static char *whereTempTriggers(Parse *pParse, Table *pTab){
Trigger *pTrig;
char *zWhere = 0;
const Schema *pTempSchema = pParse->db->aDb[1].pSchema; /* Temp db schema */
/* If the table is not located in the temp-db (in which case NULL is
** returned, loop through the tables list of triggers. For each trigger
** that is not part of the temp-db schema, add a clause to the WHERE
** expression being built up in zWhere.
*/
if( pTab->pSchema!=pTempSchema ){
sqlite3 *db = pParse->db;
for(pTrig=sqlite3TriggerList(pParse, pTab); pTrig; pTrig=pTrig->pNext){
if( pTrig->pSchema==pTempSchema ){
zWhere = whereOrName(db, zWhere, pTrig->zName);
}
}
}
if( zWhere ){
char *zNew = sqlite3MPrintf(pParse->db, "type='trigger' AND (%s)", zWhere);
sqlite3DbFree(pParse->db, zWhere);
zWhere = zNew;
}
return zWhere;
}
/*
** Generate code to drop and reload the internal representation of table
** pTab from the database, including triggers and temporary triggers.
** Argument zName is the name of the table in the database schema at
** the time the generated code is executed. This can be different from
** pTab->zName if this function is being called to code part of an
** "ALTER TABLE RENAME TO" statement.
生成代码删除和重新加载从数据库表pTab的内部表达示,
包括触发器和临时触发器。
参数zName在数据库模式中的表的名称生成的代码执行。
这可以不同于pTab - > zName如果这个函数被调用的代码的一部分“ALTER TABLE RENAME TO”声明。
*/
static void reloadTableSchema(Parse *pParse, Table *pTab, const char *zName){
Vdbe *v;
char *zWhere;
int iDb; /* Index of database containing pTab 包含pTab数据库索引*/
#ifndef SQLITE_OMIT_TRIGGER
Trigger *pTrig;
#endif
v = sqlite3GetVdbe(pParse);
if( NEVER(v==0) ) return;
assert( sqlite3BtreeHoldsAllMutexes(pParse->db) );
iDb = sqlite3SchemaToIndex(pParse->db, pTab->pSchema);
assert( iDb>=0 );
#ifndef SQLITE_OMIT_TRIGGER
/* Drop any table triggers from the internal schema. 降低任何表触发器内部模式。*/
for(pTrig=sqlite3TriggerList(pParse, pTab); pTrig; pTrig=pTrig->pNext){
int iTrigDb = sqlite3SchemaToIndex(pParse->db, pTrig->pSchema);
assert( iTrigDb==iDb || iTrigDb==1 );
sqlite3VdbeAddOp4(v, OP_DropTrigger, iTrigDb, 0, 0, pTrig->zName, 0);
}
#endif
/* Drop the table and index from the internal schema. 从内部模式中降低表和索引*/
sqlite3VdbeAddOp4(v, OP_DropTable, iDb, 0, 0, pTab->zName, 0);
/* Reload the table, index and permanent trigger schemas. 重载表、索引和不变的触发器模式*/
zWhere = sqlite3MPrintf(pParse->db, "tbl_name=%Q", zName);
if( !zWhere ) return;
sqlite3VdbeAddParseSchemaOp(v, iDb, zWhere);
#ifndef SQLITE_OMIT_TRIGGER
/* Now, if the table is not stored in the temp database, reload any temp
** triggers. Don't use IN(...) in case SQLITE_OMIT_SUBQUERY is defined.
现在，如果表没有在临时数据库中存储，那么重载任何临时触发器。
不要用IN(...)在 SQLITE_OMIT_SUBQUERY被默认的情况下。
*/
if( (zWhere=whereTempTriggers(pParse, pTab))!=0 ){
sqlite3VdbeAddParseSchemaOp(v, 1, zWhere);
}
#endif
}
