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PQsendQuery

Location

src/interfaces/libpq/fe-exec.c:1416-1421

Overview

Submits a SQL query to the PostgreSQL server asynchronously without waiting for completion, allowing the client to continue other operations while the query executes.

Definition

int PQsendQuery(PGconn *conn, const char *query)

Detailed Description

PQsendQuery is the primary asynchronous query submission function in libpq. It sends a SQL query to the PostgreSQL server and returns immediately without waiting for the query to complete. This enables non-blocking query execution, allowing applications to perform other operations while waiting for query results.

The function is essentially a wrapper around PQsendQueryInternal, passing true for the error message reset parameter. This means that any previous error messages in the connection object are cleared before sending the new query, providing a clean state for error reporting.

After calling PQsendQuery, applications typically use PQgetResult() to retrieve results when they become available, or use connection polling mechanisms to determine when results are ready.

Parameters / Member Variables

  • conn: Pointer to the PostgreSQL connection object
  • query: C string containing the SQL query to execute

Dependencies

Notes and Other Information

  • Returns 1 on successful submission, 0 on error
  • This is an exported function, part of libpq's public API
  • Resets conn->errorMessage before processing (unlike PQsendQueryContinue)
  • Essential for building responsive PostgreSQL client applications
  • Often used in combination with PQgetResult() for result retrieval
  • Supports PostgreSQL's asynchronous processing model
  • The query parameter must be a null-terminated C string
  • Does not support parameterized queries (use PQsendQueryParams for that)
  • Part of the foundation for more complex features like query pipelining

Simplified Source

int PQsendQuery(PGconn *conn, const char *query) {
    // Submit query asynchronously with error message reset
    return PQsendQueryInternal(conn, query, true);
}