/*
** While a SrcList can in general represent multiple tables and subqueries
** (as in the FROM clause of a SELECT statement) in this case it contains
** the name of a single table, as one might find in an INSERT, DELETE,
** or UPDATE statement. Look up that table in the symbol table and
** return a pointer. Set an error message and return NULL if the table
** name is not found or if any other error occurs.
**
** The following fields are initialized appropriate in pSrc:
**
** pSrc->a[0].pTab Pointer to the Table object
** pSrc->a[0].pIndex Pointer to the INDEXED BY index, if there is one
**
*/
Table *sqlite3SrcListLookup(Parse *pParse, SrcList *pSrc){
struct SrcList_item *pItem = pSrc->a;
Table *pTab;
assert( pItem && pSrc->nSrc==1 );
pTab = sqlite3LocateTableItem(pParse, 0, pItem);
sqlite3DeleteTable(pParse->db, pItem->pTab);
pItem->pTab = pTab;
if( pTab ){
pTab->nRef++;
}
if( sqlite3IndexedByLookup(pParse, pItem) ){
pTab = 0;
}
return pTab;
}
/*
** While a SrcList can in general represent multiple tables and subqueries
** (as in the FROM clause of a SELECT statement) in this case it contains
** the name of a single table, as one might find in an INSERT, DELETE,
** or UPDATE statement. Look up that table in the symbol table and
** return a pointer. Set an error message and return NULL if the table
** name is not found or if any other error occurs.
**而SrcList可以在代表多个表和子查询（如在从SELECT语句的子句）在此情况下，它含有（如在FROM SELECT语句的子句）在此情况下，它包含单个表的名称，因为可能会发现一个INSERT，DELETE或UPDATE语句。查找该表中的符号表，并返回一个指针。设置一个错误信息，如果表名没有找到返回NULL，或如果发生任何错误。
** The following fields are initialized appropriate in pSrc:
**在pSrc初始化以下字段:
** pSrc->a[0].pTab Pointer to the Table object 指向目标表
** pSrc->a[0].pIndex Pointer to the INDEXED BY index, if there is one 有INDEXED BY语句的指向INDEXED BY 索引
**
*/
Table *sqlite3SrcListLookup(Parse *pParse, SrcList *pSrc){
//函数的作用查找所有名字为pSrc的表，如果没有找到任何表，添加一个错误消息pParse - > zErrMsg并返回NULL。如果所有的表都找到，返回一个指针，指向最后一个表。
struct SrcList_item *pItem = pSrc->a;
Table *pTab;
assert( pItem && pSrc->nSrc==1 );
pTab = sqlite3LocateTable(pParse, 0, pItem->zName, pItem->zDatabase);
//这个函数定位pItem所指的表所在的数据库，表的名字，并用指针pTab指向该定位的表
sqlite3DeleteTable(pParse->db, pItem->pTab);
//功能：删除该表 ，但是还没有调用该函数
pItem->pTab = pTab;
if( pTab ){//如果这个表存在，则逐一检查这个表中的参数
pTab->nRef++;
}
if( sqlite3IndexedByLookup(pParse, pItem) ){//如果通过查找索引和该表匹配，则0表示要找的就是这个表
pTab = 0;
}
return pTab;
}
