libpg_query

C library for accessing the PostgreSQL parser outside of the server.

This library uses the actual PostgreSQL server source to parse SQL queries and return the internal PostgreSQL parse tree.

Note that this is mostly intended as a base library for https://github.com/lfittl/pg_query (Ruby) and https://github.com/lfittl/pg_query.go (Go).

You can find further background to why a query's parse tree is useful here: https://pganalyze.com/blog/parse-postgresql-queries-in-ruby.html

Installation

git clone -b 9.5-latest git://github.com/lfittl/libpg_query
cd libpg_query
make

Due to compiling parts of PostgreSQL, running make will take a bit. Expect up to 3 minutes.

For a production build, its best to use a specific git tag (see CHANGELOG).

Usage: Parsing a query

A full example that parses a query looks like this:

#include <pg_query.h>
#include <stdio.h>

int main() {
  PgQueryParseResult result;

  pg_query_init();

  result = pg_query_parse("SELECT 1");

  printf("%s\n", result.parse_tree);

  pg_query_free_parse_result(result);
}

Compile it like this:

cc -Ilibpg_query -Llibpg_query -lpg_query example.c

This will output:

[{"SELECT": {"distinctClause": null, "intoClause": null, "targetList": [{"RESTARGET": {"name": null, "indirection": null, "val": {"A_CONST": {"val": 1, "location": 7}}, "location": 7}}], "fromClause": null, "whereClause": null, "groupClause": null, "havingClause": null, "windowClause": null, "valuesLists": null, "sortClause": null, "limitOffset": null, "limitCount": null, "lockingClause": null, "withClause": null, "op": 0, "all": false, "larg": null, "rarg": null}}]

Usage: Fingerprinting a query

Fingerprinting allows you to identify similar queries that are different only because of the specific object that is being queried for (i.e. different object ids in the WHERE clause), or because of formatting.

Example:

#include <pg_query.h>
#include <stdio.h>

int main() {
  PgQueryFingerprintResult result;

  pg_query_init();

  result = pg_query_fingerprint("SELECT 1");

  printf("%s\n", result.hexdigest);

  pg_query_free_fingerprint_result(result);
}

This will output:

8e1acac181c6d28f4a923392cf1c4eda49ee4cd2

See https://github.com/lfittl/libpg_query/wiki/Fingerprinting for the full fingerprinting rules.

Usage: Parsing a PL/pgSQL function (Experimental)

A full example that parses a PL/pgSQL method looks like this:

#include <pg_query.h>
#include <stdio.h>
#include <stdlib.h>

int main() {
  PgQueryPlpgsqlParseResult result;

  pg_query_init();

  result = pg_query_parse_plpgsql(" \
  CREATE OR REPLACE FUNCTION cs_fmt_browser_version(v_name varchar, \
                                                  v_version varchar) \
RETURNS varchar AS $$ \
BEGIN \
    IF v_version IS NULL THEN \
        RETURN v_name; \
    END IF; \
    RETURN v_name || '/' || v_version; \
END; \
$$ LANGUAGE plpgsql;");

  if (result.error) {
    printf("error: %s at %d\n", result.error->message, result.error->cursorpos);
  } else {
    printf("%s\n", result.plpgsql_funcs);
  }

  pg_query_free_plpgsql_parse_result(result);

  return 0;
}

This will output:

[
{"PLpgSQL_function": {"datums": [{"PLpgSQL_var": {"refname": "found", "datatype": {"PLpgSQL_type": {"typname": "UNKNOWN"}}}}], "action": {"PLpgSQL_stmt_block": {"lineno": 1, "body": [{"PLpgSQL_stmt_if": {"lineno": 1, "cond": {"PLpgSQL_expr": {"query": "SELECT v_version IS NULL"}}, "then_body": [{"PLpgSQL_stmt_return": {"lineno": 1, "expr": {"PLpgSQL_expr": {"query": "SELECT v_name"}}}}]}}, {"PLpgSQL_stmt_return": {"lineno": 1, "expr": {"PLpgSQL_expr": {"query": "SELECT v_name || '/' || v_version"}}}}]}}}}
]

Versions

For stability, it is recommended you use individual tagged git versions, see CHANGELOG.

Current master reflects a PostgreSQL base version of 9.4, with a legacy output format.

New development is happening on 9.5-latest, which will become master in the future.

Authors

• Lukas Fittl

License

PostgreSQL server source code, used under the PostgreSQL license.
Portions Copyright (c) 1996-2016, The PostgreSQL Global Development Group
Portions Copyright (c) 1994, The Regents of the University of California

All other parts are licensed under the 3-clause BSD license, see LICENSE file for details.
Copyright (c) 2016, Lukas Fittl [email protected]