| Postgres-XC 1.1 Documentation | ||||
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Note: The following description applies both to Postgres-XC and PostgreSQL if not described explicitly.
The following commands are available to access the database from the body of a PL/Tcl function:
spi_exec ?-count n? ?-array name? command ?loop-body?        Executes an SQL command given as a string.  An error in the command
        causes an error to be raised.  Otherwise, the return value of spi_exec
        is the number of rows processed (selected, inserted, updated, or
        deleted) by the command, or zero if the command is a utility
        statement.  In addition, if the command is a SELECT statement, the
        values of the selected columns are placed in Tcl variables as
        described below.
       
        The optional -count value tells
        spi_exec the maximum number of rows
        to process in the command.  The effect of this is comparable to
        setting up a query as a cursor and then saying FETCH n.
       
If the command is a SELECT statement, the values of the result columns are placed into Tcl variables named after the columns. If the -array option is given, the column values are instead stored into the named associative array, with the column names used as array indexes.
        If the command is a SELECT statement and no loop-body
        script is given, then only the first row of results are stored into
        Tcl variables; remaining rows, if any, are ignored.  No storing occurs
        if the
        query returns no rows.  (This case can be detected by checking the
        result of spi_exec.)  For example:
spi_exec "SELECT count(*) AS cnt FROM pg_proc"
will set the Tcl variable $cnt to the number of rows in the pg_proc system catalog.
If the optional loop-body argument is given, it is a piece of Tcl script that is executed once for each row in the query result. (loop-body is ignored if the given command is not a SELECT.) The values of the current row's columns are stored into Tcl variables before each iteration. For example:
spi_exec -array C "SELECT * FROM pg_class" {
    elog DEBUG "have table $C(relname)"
}will print a log message for every row of pg_class. This feature works similarly to other Tcl looping constructs; in particular continue and break work in the usual way inside the loop body.
If a column of a query result is null, the target variable for it is "unset" rather than being set.
spi_prepare query typelistPostgres-XC does not support PREPARE reature yet. This will be supported in the future releases.
spi_execp ?-count n? ?-array name? ?-nulls string? queryid ?value-list? ?loop-body?Note: The following description applies only to Postgres-XC
Postgres-XC does not support PREPARE in the current release. This may be supported in the future releases.
spi_lastoid        Returns the OID of the row inserted by the last
        spi_exec or spi_execp, if the
        command was a single-row INSERT and the modified
        table contained OIDs.  (If not, you get zero.)
       
Note: The following description applies only to Postgres-XC
Please note that OID is maintained locally at each Datanode and Coordinator.
quote string        Doubles all occurrences of single quote and backslash characters
        in the given string.  This can be used to safely quote strings
        that are to be inserted into SQL commands given
        to spi_exec or
        spi_prepare.
        For example, think about an SQL command string like:
"SELECT '$val' AS ret"
where the Tcl variable val actually contains doesn't. This would result in the final command string:
SELECT 'doesn't' AS ret
        which would cause a parse error during
        spi_exec or
        spi_prepare.
        To work properly, the submitted command should contain:
SELECT 'doesn''t' AS ret
which can be formed in PL/Tcl using:
"SELECT '[ quote $val ]' AS ret"
        One advantage of spi_execp is that you don't
        have to quote parameter values like this, since the parameters are never
        parsed as part of an SQL command string.
       
elog level msgEmits a log or error message. Possible levels are DEBUG, LOG, INFO, NOTICE, WARNING, ERROR, and FATAL. ERROR raises an error condition; if this is not trapped by the surrounding Tcl code, the error propagates out to the calling query, causing the current transaction or subtransaction to be aborted. This is effectively the same as the Tcl error command. FATAL aborts the transaction and causes the current session to shut down. (There is probably no good reason to use this error level in PL/Tcl functions, but it's provided for completeness.) The other levels only generate messages of different priority levels. Whether messages of a particular priority are reported to the client, written to the server log, or both is controlled by the log_min_messages and client_min_messages configuration variables. See Chapter 17 for more information.