sql: add pg_conversion

[BramGruneir]

PGAdmin issues the following query:

  SELECT cl.relkind, 
         COALESCE(cin.nspname, cln.nspname) AS nspname, 
         COALESCE(ci.relname, cl.relname) AS relname, 
         cl.relname AS indname 
  FROM pg_class AS cl 
  JOIN pg_namespace AS cln 
    ON cl.relnamespace = cln.oid 
  LEFT JOIN pg_index AS ind 
    ON ind.indexrelid = cl.oid 
  LEFT JOIN pg_class AS ci 
    ON ind.indrelid = ci.oid 
  LEFT JOIN pg_namespace AS cin 
    ON ci.relnamespace = cin.oid 
  WHERE (cl.oid IN (
    SELECT objid 
    FROM pg_shdepend 
    WHERE refobjid = 2901009604::OID
  )) 
  AND (cl.oid > none::OID) 
UNION ALL 
  SELECT 'n', 
         NULL, 
         nspname, 
         NULL 
  FROM pg_namespace AS nsp 
  WHERE (nsp.oid IN (
    SELECT objid 
    FROM pg_shdepend 
    WHERE refobjid = 2901009604::OID
  )) 
  AND (nsp.oid > none::OID) 
UNION ALL 
  SELECT CASE WHEN typtype = 'd' 
           THEN 'd' 
           ELSE 'y' 
        END, 
        NULL, 
        typname, 
        NULL 
  FROM pg_type AS ty 
  WHERE (ty.oid IN (
    SELECT objid 
    FROM pg_shdepend 
    WHERE refobjid = 2901009604::OID
  )) 
  AND (ty.oid > none::OID) 
UNION ALL
  SELECT 'C', 
         NULL, 
         conname, 
         NULL 
  FROM pg_conversion AS co 
  WHERE (co.oid IN (
    SELECT objid 
    FROM pg_shdepend 
    WHERE refobjid = 2901009604::OID
  )) 
  AND (co.oid > none::OID) 
UNION ALL 
  SELECT CASE WHEN prorettype = 2279 
           THEN 'T' 
           ELSE 'p' 
        END, 
        NULL, 
        proname, 
        NULL 
  FROM pg_proc AS pr 
  WHERE (pr.oid IN (
    SELECT objid 
    FROM pg_shdepend 
    WHERE refobjid = 2901009604::OID
  )) 
  AND (pr.oid > none::OID) 
UNION ALL 
  SELECT 'o', 
         NULL, 
         (
           (
             (
               (oprname || '('::TEXT) 
                 || COALESCE(tl.typname, ''::TEXT)
             ) || CASE WHEN (tl.oid IS NOT NULL) AND (tr.oid IS NOT NULL) 
               THEN ','::TEXT END
           ) || COALESCE(tr.typname, ''::TEXT)
          ) || ')'::TEXT, 
          NULL 
  FROM pg_operator AS op 
  LEFT JOIN pg_type AS tl 
    ON tl.oid = op.oprleft 
  LEFT JOIN pg_type AS tr 
    ON tr.oid = op.oprright 
  WHERE (op.oid IN (
    SELECT objid 
    FROM pg_shdepend 
    WHERE refobjid = 2901009604::OID
  )) 
  AND (op.oid > none::OID) 
  ORDER BY 1, 2, 3

See https://www.postgresql.org/docs/current/static/catalog-pg-conversion.html for details.