- Vytvoril/a D2000 Dev Team, naposledy zmenil/a D2000 Doc Team dňa okt 03, 2021
SQL_BINDIN action
Function
The action specifies values of the parameters and executes a SQL command SELECT prepared by action SQL_PREPARE, if the latter action used parameterization and a keyword BINDOUT.
Declaration
SQL_BINDIN handleIdent_Int, retCodeIdent_Int, _Par1, _Par2, ... SQL_BINDIN handleIdent_Int, retCodeIdent_Int, _VarRowIdent
Parameters
| handleIdent_Int | in | Identifier - the unique number (handle) of a connection. |
| retCodeIdent_Int | out | Return code identifier. |
| _Par1, _Par2, ... | in | List of objects, constants or local variables, which will specify the values of parameters of parameterized SQL command SELECT. |
| _VarRowIdent | in | Reference to a row of local variable of the Record type or to a row of structured variable. The row's values will specify the values of parameters of parameterized SQL command SELECT. |
Return code
The value of the parameter transHandle_Int. See the table of error codes. It is possible to get extended error information.
Description
Reading a database by the command SELECT is implemented in two or three phases.
The first (preparatory) phase is executed by the action SQL_PREPARE. The command SELECT, defined by a value of the expression selectStringExpr, is prepared (and if the keyword BINDOUT is not used, then also executed) in the database.
If the keyword BINDOUT was used, it means that the SQL SELECT command was parameterized, and the second phase is needed. The command SQL_BINDIN must be used to specify the values of the input parameters and execute the SQL statement.
The last phase is the sequential reading of the rows, prepared by the command SELECT, using the action SQL_FETCH.
Note: By using parameterization it is possible to make the work of SQL database easier, because the preparation (compilation) of parameterized SQL query will be performed only once (by the action SQL_PREPARE). Consequently the values of parameters must be specified by the action SQL_BINDIN (which will also execute the SQL command) and then the action SQL_FETCH may be called once or more times to obtain the results. Then it is possible to set new values of the parameters and re-execute the SQL command by repeating the action SQL_BINDIN and obtain the new results by one or more calls of the action SQL_FETCH.
By proper setting of the database parameters (e.g. Oracle: session_cached_cursors) it is possible to ensure recycling of cursors (compiled statements) between the calls of SQL_PREPARE.
The first (preparatory) phase is executed by the action SQL_PREPARE. The command SELECT, defined by a value of the expression selectStringExpr, is prepared (and if the keyword BINDOUT is not used, then also executed) in the database.
If the keyword BINDOUT was used, it means that the SQL SELECT command was parameterized, and the second phase is needed. The command SQL_BINDIN must be used to specify the values of the input parameters and execute the SQL statement.
The last phase is the sequential reading of the rows, prepared by the command SELECT, using the action SQL_FETCH.
Note: By using parameterization it is possible to make the work of SQL database easier, because the preparation (compilation) of parameterized SQL query will be performed only once (by the action SQL_PREPARE). Consequently the values of parameters must be specified by the action SQL_BINDIN (which will also execute the SQL command) and then the action SQL_FETCH may be called once or more times to obtain the results. Then it is possible to set new values of the parameters and re-execute the SQL command by repeating the action SQL_BINDIN and obtain the new results by one or more calls of the action SQL_FETCH.
By proper setting of the database parameters (e.g. Oracle: session_cached_cursors) it is possible to ensure recycling of cursors (compiled statements) between the calls of SQL_PREPARE.
Example
Work with a database (actions SQL_ ...)
INT _handle ; handle to database
INT _retCode ; return code
TEXT _name ; product name
TEXT _type ; product type
; parameterized SQL command
TEXT _sql = "SELECT Name, Type FROM Products WHERE ID>= #PAR# AND ID<= #PAR#"
SQL_CONNECT MyDatabase, _handle, _retCode
SQL_PREPARE _handle, _retCode, _sql BINDOUT _name, _type
SQL_BINDIN _handle, _retCode, 1, 100 ; read all products between 1 and 100
DO_LOOP
SQL_FETCH _handle, _retCode
EXIT_LOOP _retCode # _ERR_NO_ERROR
; data processing goes here
END_LOOP
SQL_FREE _handle
SQL_DISCONNECT _handle
Related topics
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