- Vytvoril/a D2000 Dev Team, naposledy zmenené nov 22, 2019
SQL_SELECT action
SQL_SELECT dbObjIdent, retCodeIdent_Int, [maxRowsIdent_Int], selectIdent_String [TRANS transHandle_Int] BIND ...
SQL_SELECT connectString, retCodeIdent_Int, [maxRowsIdent_Int], selectIdent_String ON dbManIdent BIND ...
BIND _locVar1, _locVar2, ...
BIND _locVarRowIdent
BIND _locVarRecordIdent
| dbObjIdent | in | Reference to an object of Database or Database table type. |
| connectString | in | Identifier of Text type or a text constant containing a connect string to the database. |
| retCodeIdent_Int | out | Identifier of Int type - return code. |
| maxRowsIdent_Int | in | Identifier of Int type - number of rows read en bloc (if it is not entered the default value is 1). |
| selectIdent_String | in | Identifier of String type. |
| _locVar1, _locVar2, ... | in | List of local variable. |
| _locVarRowIdent | in | Reference to row of local variable of Record type. |
| _locVarRecordIdent | in | Identifier of local variable of Record type. |
A database, in which the SQL command SELECT will be executed, can be defined by:
- parameter dbObjIdent - represents the object of Database or Table type. User can enter the parameter (optional) transHandle_Int that defines a database connection (the value of parameter has been gained by previous calling the action DB_TRANS_OPEN), within it the SQL command will be executed,
If the parameter transHandle_Int is not defined, SQL command will be executed on one of the predefined database connections. - parameter connectString (described on page SQL_CONNECT action). It is necessary to specify the process DB Manager that will execute the SQL command.
The command SELECT is defined by value of parameter selectIdent_String. According to number of columns of SELECT command should be chosen the proper variant to show its result through the obligatory key word BIND. The meaning and explanation of the variants is mentioned in action SQL_PREPARE.
An optional identifier maxRowsIdent_Int defines the row counts of select which will be returned. If it is not defined its value is 1. The number of the rows that can be read depends also on the variant BIND. Details are in the description of action SQL_FETCH.
Maximum number of returned rows is limited by a Database configuration parameter Maximum returned rows. If number of available rows exceeds this limit, the local structure _locVarRecordIdent will contain first Maximum returned rows and retCodeIdent_Int will be set to error code _ERR_DATABASE_ROWS_LIMIT.
Note
he values returned byt the SQL statement are inserted into local variables according to their order (1st value to the first bound variable, 2nd to the second, etc.). This also applies when inserting into a local structured variable (i.e. column names are not taken into account). Potentially dangerous are SELECTs of the "SELECT *" type - if the order of the columns in the database differs from the order of the columns in the structured variable, the values will be inserted in the wrong columns. Therefore, we recommend explicitly naming columns in SQL query (SELECT COL1, COL2, COL3 ...).
If retrieving data from a single table or view, use DBS_READ instead of SQL_SELECT.
A procedure Demo1 represents various (not all) variants of SQL_SELECT action.
The procedures Demo2 and Demo3 have the same function. Demo2 is implemented through the SQL_SELECT action and Demo3 is implemented by SQL_CONNECT action, SQL_PREPARE action, SQL_FETCH action and SQL_DISCONNECT action.
PROCEDURE Demo1
INT _retCod
INT _maxId
; select through the object of Database type
SQL_SELECT gnat_test, _retCode,, "select max(id) from OBJLIST" BIND _maxId
IF _retCode = _ERR_NO_ERROR THEN
; variable _maxId contains the value
ELSE
; error
ENDIF
; select through the object of Table type
SQL_SELECT DB.OBJLIST, _retCode,, "select max(id) from OBJLIST" BIND _maxId
IF _retCode = _ERR_NO_ERROR THEN
; variable _maxId contains the value
ELSE
; error
ENDIF
INT _transHandle
; opening of the transaction through the object of Database type
DB_TRANS_OPEN gnat_test, _transHandle, _retCode
IF _retCode = _ERR_NO_ERROR THEN
; transaction has been opened
; select within the transaction
SQL_SELECT DB.OBJLIST, _retCode,, "select max(id) from OBJLIST" TRANS _transHandle BIND _maxId
IF _retCode = _ERR_NO_ERROR THEN
; variable _maxId contains the value
ELSE
; error
ENDIF
DB_TRANS_CLOSE _transHandle
ELSE
; error
ENDIF
; select with the connection
SQL_SELECT "connection String", _retCode,, "select max(id) from OBJLIST" ON SELF.DBM BIND _maxId
IF _retCode = _ERR_NO_ERROR THEN
; variable _maxId contains the value
ELSE
; error
ENDIF
END Demo1
PROCEDURE Demo2(INT _maxId)
INT _retCode
_maxId := %SetInvalid(0)
; select through the object of Database type
SQL_SELECT gnat_test, _retCode,, "select max(id) from OBJLIST" BIND _maxId
IF _retCode = _ERR_NO_ERROR THEN
; variable _maxId contains the value
ELSE
; error
ENDIF
END Demo2
PROCEDURE Demo3(INT _maxId)
INT _retCode
INT _handle
_maxId := %SetInvalid(0)
;
SQL_CONNECT gnat_test, _handle, _retCode
IF _retCode <> _ERR_NO_ERROR THEN
RETURN ; error
ENDIF
SQL_PREPARE _handle, _retCode, "select max(id) from OBJLIST" BIND _maxId
IF _retCode <> _ERR_NO_ERROR THEN
RETURN ; error
ENDIF
SQL_FETCH _handle, _retCode
IF _retCode <> _ERR_NO_ERROR THEN
RETURN ; error
ENDIF
SQL_DISCONNECT _handle
END Demo3
BEGIN
CALL Demo1
INT _max
CALL Demo2(_max)
CALL Demo3(_max)
END
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