Have chDB use postgres session's TimeZone

CHANGELOG.md

@@ -9,12 +9,21 @@ All notable changes to this project will be documented in this file. It uses the
 
 ## Unreleased
 
+### ⚡ Improvements
+
+*   Preserve declared fractional-second precision when mapping `time`,
+    `timestamp`, and `timestamptz` columns to chDB types ([#101]).
+
 ### 🐞 Bug Fixes
 
+*   Use PostgreSQL session `TimeZone` in chDB so `COPY FROM` preserves
+    `timestamp` wall-clock values when input omits time zone ([#101]).
 *   Preserve Azure SAS tokens between schema inference and data loading in
     `CREATE TABLE ... COPY FROM` ([#103]).
 *   Fix GCC 15 build failures caused by discarded `const` qualifiers ([#103]).
 
+  [#101]: https://github.com/ClickHouse/pg_chdb/pull/101
+    "ClickHouse/pg_chdb#101 Have chDB use postgres session's TimeZone"
   [#103]: https://github.com/ClickHouse/pg_chdb/pull/103
     "ClickHouse/pg_chdb#103 Use const more"
 

doc/chdb_hook.md

@@ -483,7 +483,7 @@ those you need.
 | bytea            | String                                 |                                                                        |
 | date             | Date32                                 |                                                                        |
 | time             | Time64(6)                              | Override with `String` for formats that don't support times.           |
-| timestamp        | DateTime64(6, 'UTC')                   | Converted from session time zone.                                      |
+| timestamp        | DateTime64(6)                          | Converted from session time zone.                                      |
 | timestamptz      | DateTime64(6, 'UTC')                   |                                                                        |
 | interval         | String                                 | Override with an `Interval` unit such as `IntervalDay`.                |
 | uuid             | UUID                                   |                                                                        |

src/helper.c

@@ -26,6 +26,8 @@
 #include "utils/palloc.h"
 #include "utils/wait_event.h"
 
+#include "pg-clickhouse.h"
+
 #include "helper.h"
 #include "setup.h"
 
@@ -367,6 +369,8 @@ build_setup(
     appendBinaryStringInfo(buf, (char*)&ctx->max_threads, sizeof(ctx->max_threads));
     appendBinaryStringInfo(buf, (char*)&ctx->max_parsers, sizeof(ctx->max_parsers));
 
+    /* timestamp maps to DateTime64 without time zone, read in this zone */
+    append_string(buf, pgch_session_timezone());
     append_string(buf, query);
 
     uint16_t count = (uint16_t)nparams;

src/helper/chdb_helper.c

@@ -309,7 +309,8 @@ setup_session(
     chdb_connection conn,
     uint16_t max_mem,
     uint16_t max_threads,
-    uint16_t max_parsers
+    uint16_t max_parsers,
+    str timezone
 ) {
     char settings[1024];
     snprintf(
@@ -321,10 +322,12 @@ setup_session(
         "output_format_native_encode_types_in_binary_format=0,"
         "date_time_output_format='iso',"
         "max_threads=%" PRIu16 ",max_parsing_threads=%" PRIu16
-        ",max_memory_usage=%" PRIu64,
+        ",max_memory_usage=%" PRIu64 ",session_timezone='%.*s'",
         max_threads,
         max_parsers,
-        (uint64_t)max_mem * 1024 * 1024
+        (uint64_t)max_mem * 1024 * 1024,
+        (int)timezone.len,
+        timezone.data
     );
     chdb_result* res = chdb_query(conn, settings, native_format);
     const char* err  = chdb_result_error(res);
@@ -346,6 +349,7 @@ main(void) {
     uint16_t max_mem     = take2(&cur);
     uint16_t max_threads = take2(&cur);
     uint16_t max_parsers = take2(&cur);
+    str timezone         = take_str(&cur);
     str query            = take_str(&cur);
     uint16_t npar        = take2(&cur);
 
@@ -380,7 +384,7 @@ main(void) {
      * Unfortunately, setting via argv doesn't work, so we have to set them a
      * an initial query. https://github.com/chdb-io/chdb-core/issues/191
      */
-    int status = setup_session(*conn, max_mem, max_threads, max_parsers);
+    int status = setup_session(*conn, max_mem, max_threads, max_parsers, timezone);
 
     if (!status) {
         switch (cmd_type) {

src/hook/copy.c

@@ -89,8 +89,8 @@ structure_for_attnums(TupleDesc desc, List* attnums) {
 }
 
 /*
- * Return a copy of `structure` with every bare `type` clause replaced with
- * `String`.
+ * Return a copy of `structure` with every bare `type` clause, along with any
+ * parameters it takes, replaced with `String`.
  */
 static char*
 structure_as_string(const char* structure, const char* type) {
@@ -104,20 +104,25 @@ structure_as_string(const char* structure, const char* type) {
             quoted = !quoted;
         }
         if (!quoted && strncmp(pos, type, len) == 0 && pos > structure &&
-            (pos[-1] == ' ' || pos[-1] == '(') &&
-            (pos[len] == '\0' || pos[len] == ',' || pos[len] == ')')) {
-            appendStringInfoString(&buf, "String");
-            pos += len;
-        } else {
-            appendStringInfoChar(&buf, *pos++);
+            (pos[-1] == ' ' || pos[-1] == '(')) {
+            const char* end = pos + len;
+            if (*end == '(' && strchr(end, ')')) {
+                end = strchr(end, ')') + 1;
+            }
+            if (*end == '\0' || *end == ',' || *end == ')') {
+                appendStringInfoString(&buf, "String");
+                pos = end;
+                continue;
+            }
         }
+        appendStringInfoChar(&buf, *pos++);
     }
     return buf.data;
 }
 
 /*
  * Returns true if `format` is one of the formats lacking Time64 support.
- * In such cases, `Time64(6)` should be replaced with `String`.
+ * In such cases, `Time64` should be replaced with `String`.
  */
 static bool
 format_lacks_time64(const char* format) {
@@ -152,7 +157,7 @@ chdb_copy(chdbCopyContext* ctx) {
             ctx->structure = structure_as_string(ctx->structure, "UUID");
         }
         if (format_lacks_time64(ctx->format)) {
-            ctx->structure = structure_as_string(ctx->structure, "Time64(6)");
+            ctx->structure = structure_as_string(ctx->structure, "Time64");
         }
     }
 

src/setup.h

@@ -24,6 +24,7 @@ typedef struct chdbHelperContext {
  * Fields are native endian.
  *
  *   chdbHelperContext      command type, settings
+ *   string                 session_timezone
  *   string                 query
  *   uint16                 parameter count
  *   string                 parameter name and value, repeated

t/structure.pl

@@ -302,7 +302,7 @@
         qq{COPY datetime FROM 'file://$dir/nonesuch.csv'},
         qr/nonesuch.csv doesn't exist/,
         qr[\QSELECT * FROM file],
-        qr[\Q structure: "ts Nullable(DateTime64(6, 'UTC')), tsn Nullable(DateTime64(6, 'UTC')), tstz DateTime64(6, 'UTC'), tstzn DateTime64(6, 'UTC'), date Date32, time Time64(6), timen Time64(6), ttz String, ttzn String, ival String" }],
+        qr[\Q structure: "ts Nullable(DateTime64(6)), tsn Nullable(DateTime64(3)), tstz DateTime64(6, 'UTC'), tstzn DateTime64(4, 'UTC'), date Date32, time Time64(6), timen Time64(3), ttz String, ttzn String, ival String" }],
     );
 
     $node->psql(postgres => q{
@@ -324,7 +324,7 @@
         qq{COPY datetime_arrays FROM 'file://$dir/nonesuch.csv'},
         qr/nonesuch.csv doesn't exist/,
         qr[\QSELECT * FROM file],
-        qr[\Q structure: "ts Array(Nullable(DateTime64(6, 'UTC'))), tsn Array(Nullable(DateTime64(6, 'UTC'))), tstz Array(Nullable(DateTime64(6, 'UTC'))), tstzn Array(Nullable(DateTime64(6, 'UTC'))), date Array(Nullable(Date32)), time Array(Nullable(Time64(6))), timen Array(Nullable(Time64(6))), ttz Array(Nullable(String)), ttzn Array(Nullable(String)), ival Array(Nullable(String))" }],
+        qr[\Q structure: "ts Array(Nullable(DateTime64(6))), tsn Array(Nullable(DateTime64(3))), tstz Array(Nullable(DateTime64(6, 'UTC'))), tstzn Array(Nullable(DateTime64(4, 'UTC'))), date Array(Nullable(Date32)), time Array(Nullable(Time64(6))), timen Array(Nullable(Time64(3))), ttz Array(Nullable(String)), ttzn Array(Nullable(String)), ival Array(Nullable(String))" }],
     );
 }
 

test/expected/timestamp.out

@@ -146,6 +146,72 @@ SELECT pg_read_file(:'tsv_path');
 
 (1 row)
 
+/************************ No offset ************************/
+-- Text without offset reads as wall clock in Postgres timezone for timestamp,
+-- UTC for timestamptz. ts stays 12:00 under every timezone.
+\set naive_path :temp_dir /naive.tsv
+\set naive_url file:// :naive_path
+CREATE TABLE naive (id INT, ts TEXT, tstz TEXT);
+INSERT INTO naive VALUES (1, '2026-08-28 12:00:00', '2026-08-28 12:00:00');
+COPY naive TO :'naive_url';
+SET timezone TO 'America/Los_Angeles';
+TRUNCATE dt2;
+COPY dt2 FROM :'naive_url';
+SELECT * FROM dt2;
+ id |         ts          |          tstz          
+----+---------------------+------------------------
+  1 | 2026-08-28 12:00:00 | 2026-08-28 05:00:00-07
+(1 row)
+
+SET timezone TO 'Asia/Tokyo';
+TRUNCATE dt2;
+COPY dt2 FROM :'naive_url';
+SELECT * FROM dt2;
+ id |         ts          |          tstz          
+----+---------------------+------------------------
+  1 | 2026-08-28 12:00:00 | 2026-08-28 21:00:00+09
+(1 row)
+
+-- Fixed offset, which chDB spells Fixed/UTC-07:00:00
+SET TIME ZONE -7;
+TRUNCATE dt2;
+COPY dt2 FROM :'naive_url';
+SELECT * FROM dt2;
+ id |         ts          |          tstz          
+----+---------------------+------------------------
+  1 | 2026-08-28 12:00:00 | 2026-08-28 05:00:00-07
+(1 row)
+
+SET timezone TO 'UTC';
+/************************ Declared precision ************************/
+-- Inferred structure takes fractional digits from column typmod.
+CREATE TABLE precisions (
+    ts   TIMESTAMP(3)   NOT NULL,
+    tstz TIMESTAMPTZ(1) NOT NULL,
+    t    TIME(4)        NOT NULL,
+    tn   TIME(2)            NULL
+);
+INSERT INTO precisions
+VALUES ('2026-07-23 20:43:27.363', '2026-07-23 20:43:50.9Z', '13:45:24.2821', '13:45:24.28');
+COPY precisions TO :'tsv_url';
+SELECT pg_read_file(:'tsv_path');
+                                    pg_read_file                                     
+-------------------------------------------------------------------------------------
+ 2026-07-23T20:43:27.363Z        2026-07-23T20:43:50.9Z  13:45:24.2821   13:45:24.28+
+
+(1 row)
+
+-- Parquet replaces parameterized Time64 with String.
+\set parquet_url file:// :temp_dir /precisions.parquet
+COPY precisions TO :'parquet_url' (format 'Parquet');
+TRUNCATE precisions;
+COPY precisions FROM :'parquet_url' (format 'Parquet');
+SELECT * FROM precisions;
+           ts            |           tstz           |       t       |     tn      
+-------------------------+--------------------------+---------------+-------------
+ 2026-07-23 20:43:27.363 | 2026-07-23 20:43:50.9+00 | 13:45:24.2821 | 13:45:24.28
+(1 row)
+
 /************************ Default scales ************************/
 -- A DateTime64 or Time64 named without a scale takes chDB's default of
 -- milliseconds, truncating the microseconds Postgres holds.

test/sql/timestamp.sql

@@ -76,6 +76,54 @@ SELECT pg_read_file(:'tsv_path');
 COPY date_times TO :'tsv_url' (structure 'id Int8, ts DateTime64(3, ''Japan''), tstz DateTime64(3, ''America/New_York'')');
 SELECT pg_read_file(:'tsv_path');
 
+/************************ No offset ************************/
+-- Text without offset reads as wall clock in Postgres timezone for timestamp,
+-- UTC for timestamptz. ts stays 12:00 under every timezone.
+\set naive_path :temp_dir /naive.tsv
+\set naive_url file:// :naive_path
+CREATE TABLE naive (id INT, ts TEXT, tstz TEXT);
+INSERT INTO naive VALUES (1, '2026-08-28 12:00:00', '2026-08-28 12:00:00');
+COPY naive TO :'naive_url';
+
+SET timezone TO 'America/Los_Angeles';
+TRUNCATE dt2;
+COPY dt2 FROM :'naive_url';
+SELECT * FROM dt2;
+
+SET timezone TO 'Asia/Tokyo';
+TRUNCATE dt2;
+COPY dt2 FROM :'naive_url';
+SELECT * FROM dt2;
+
+-- Fixed offset, which chDB spells Fixed/UTC-07:00:00
+SET TIME ZONE -7;
+TRUNCATE dt2;
+COPY dt2 FROM :'naive_url';
+SELECT * FROM dt2;
+SET timezone TO 'UTC';
+
+/************************ Declared precision ************************/
+-- Inferred structure takes fractional digits from column typmod.
+CREATE TABLE precisions (
+    ts   TIMESTAMP(3)   NOT NULL,
+    tstz TIMESTAMPTZ(1) NOT NULL,
+    t    TIME(4)        NOT NULL,
+    tn   TIME(2)            NULL
+);
+
+INSERT INTO precisions
+VALUES ('2026-07-23 20:43:27.363', '2026-07-23 20:43:50.9Z', '13:45:24.2821', '13:45:24.28');
+
+COPY precisions TO :'tsv_url';
+SELECT pg_read_file(:'tsv_path');
+
+-- Parquet replaces parameterized Time64 with String.
+\set parquet_url file:// :temp_dir /precisions.parquet
+COPY precisions TO :'parquet_url' (format 'Parquet');
+TRUNCATE precisions;
+COPY precisions FROM :'parquet_url' (format 'Parquet');
+SELECT * FROM precisions;
+
 /************************ Default scales ************************/
 -- A DateTime64 or Time64 named without a scale takes chDB's default of
 -- milliseconds, truncating the microseconds Postgres holds.