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| author | Tom Lane <tgl@sss.pgh.pa.us> | 2022-08-17 11:12:35 -0400 |
|---|---|---|
| committer | Tom Lane <tgl@sss.pgh.pa.us> | 2022-08-17 11:12:35 -0400 |
| commit | efd0c16becbf45e3b0215e124fde75fee8fcbce4 (patch) | |
| tree | 4583c8e845ce18ae4a6c6b4c008a4989c514b3cb /src/backend/commands/statscmds.c | |
| parent | 4a319fce7671ffbe2a730f79529b7a2ef3794d41 (diff) | |
| download | postgresql-efd0c16becbf45e3b0215e124fde75fee8fcbce4.tar.gz postgresql-efd0c16becbf45e3b0215e124fde75fee8fcbce4.zip | |
Avoid using list_length() to test for empty list.
The standard way to check for list emptiness is to compare the
List pointer to NIL; our list code goes out of its way to ensure
that that is the only representation of an empty list. (An
acceptable alternative is a plain boolean test for non-null
pointer, but explicit mention of NIL is usually preferable.)
Various places didn't get that memo and expressed the condition
with list_length(), which might not be so bad except that there
were such a variety of ways to check it exactly: equal to zero,
less than or equal to zero, less than one, yadda yadda. In the
name of code readability, let's standardize all those spellings
as "list == NIL" or "list != NIL". (There's probably some
microscopic efficiency gain too, though few of these look to be
at all performance-critical.)
A very small number of cases were left as-is because they seemed
more consistent with other adjacent list_length tests that way.
Peter Smith, with bikeshedding from a number of us
Discussion: https://postgr.es/m/CAHut+PtQYe+ENX5KrONMfugf0q6NHg4hR5dAhqEXEc2eefFeig@mail.gmail.com
Diffstat (limited to 'src/backend/commands/statscmds.c')
| -rw-r--r-- | src/backend/commands/statscmds.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/src/backend/commands/statscmds.c b/src/backend/commands/statscmds.c index 7c62bebfd2d..55216d28916 100644 --- a/src/backend/commands/statscmds.c +++ b/src/backend/commands/statscmds.c @@ -339,7 +339,7 @@ CreateStatistics(CreateStatsStmt *stmt) if ((list_length(stmt->exprs) == 1) && (list_length(stxexprs) == 1)) { /* statistics kinds not specified */ - if (list_length(stmt->stat_types) > 0) + if (stmt->stat_types != NIL) ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), errmsg("when building statistics on a single expression, statistics kinds may not be specified"))); @@ -391,7 +391,7 @@ CreateStatistics(CreateStatsStmt *stmt) * automatically. This allows calculating good estimates for stats that * consider per-clause estimates (e.g. functional dependencies). */ - build_expressions = (list_length(stxexprs) > 0); + build_expressions = (stxexprs != NIL); /* * Check that at least two columns were specified in the statement, or |