Description

pg_execute submits a command to the PostgreSQL server.

If the command is not a SELECT statement, the number of rows affected by the command is returned. If the command is an INSERT statement and a single row is inserted, the OID of the inserted row (if available) is stored in the variable oidVar if the optional -oid argument is supplied.

If the command is a SELECT statement, then, for each row in the result, the row values are stored in the arrayVar variable, if supplied, using the column names as the array indices, else in variables named by the column names, and then the optional procedure is executed if supplied. (Omitting the procedure probably makes sense only if the query will return a single row.) The number of rows selected is returned.

The procedure can use the Tcl commands break, continue, and return with the expected behavior. Note that if the procedure executes return, then pg_execute does not return the number of affected rows.

pg_execute is a newer command which provides a superset of the features of pg_select and can replace pg_exec in many cases where access to the result handle is not needed.

Arguments

Return Value

The number of rows affected or returned by the command.

A Tcl error will be thrown if an error occurs communicating with the database, or if there is an error processing the query. Note that this differs from pg_exec, which will not throw a Tcl error for a query which generates a database error. A Tcl error will also be thrown if a procedure body is supplied and its execution results in a Tcl error.

For database server handled errors, pg_execute will throw a Tcl error and the error message will be a two-element list. The first element is an error code, such as PGRES_FATAL_ERROR, and the second element is the database server error text. Unfortunately, other errors also result in a Tcl error being thrown but the error message is not a list - just the message text, so the list form of the error message cannot be assumed.

Notes

pg_execute cannot be used to start a COPY because it doesn't return a result handle. You must use pg_exec to start a COPY.

This command uses or emulates the PostgreSQL libpq function PQexec.

Examples

In the following examples, error checking with catch has been omitted for clarity.

Insert a row and save the OID in result_oid, assuming the mytable was created using WITH OIDS:

pg_execute -oid result_oid $conn "INSERT INTO mytable VALUES (1);"

Print the columns item and value from each row:

pg_execute -array d $conn "SELECT item, value FROM mytable" {
    puts "Item=$d(item) Value=$d(value)"
}

Find the maximum and minimum values and store them in $s(max) and $s(min):

pg_execute -array s $conn "SELECT max(value) AS max, min(value) AS min FROM mytable"

Find the maximum and minimum values and store them in $max and $min:

pg_execute $conn "SELECT max(value) AS max, min(value) AS min FROM mytable"