From 4f2151348d89f9417d161729b5b717d32804d702 Mon Sep 17 00:00:00 2001 From: "Chao Li (Evan)" Date: Wed, 6 May 2026 14:14:03 +0800 Subject: [PATCH v2] COPY JSON: use trailing commas in FORCE_ARRAY output Change COPY TO ... FORMAT JSON, FORCE_ARRAY output to place commas at the end of each array element line, instead of at the beginning of the next line. Previously, output looked like this: ``` [ {"id":1} ,{"id":2} ] ``` This is valid JSON, but it is an unusual formatting style and can be surprising to readers. Make it emit the more conventional form instead: ``` [ {"id":1}, {"id":2} ] ``` Implement this without buffering the whole result by adjusting how JSON rows are terminated and how the separator is emitted between rows. Update the regression test output accordingly. Author: Chao Li Reviewed-by: Ayush Tiwari Reviewed-by: Daniel Gustafsson Reviewed-by: Alex Guo Discussion: https://postgr.es/m/DFAC4097-2559-4DED-B7D5-EB53B02E9DA3@gmail.com --- src/backend/commands/copyto.c | 29 ++++++++++++++++++++++++----- src/test/regress/expected/copy.out | 24 ++++++++++++------------ 2 files changed, 36 insertions(+), 17 deletions(-) diff --git a/src/backend/commands/copyto.c b/src/backend/commands/copyto.c index 85d15353647..e98a15dcd64 100644 --- a/src/backend/commands/copyto.c +++ b/src/backend/commands/copyto.c @@ -156,6 +156,7 @@ static void CopySendData(CopyToState cstate, const void *databuf, int datasize); static void CopySendString(CopyToState cstate, const char *str); static void CopySendChar(CopyToState cstate, char c); static void CopySendEndOfRow(CopyToState cstate); +static void CopySendTextLikeLineTerminator(CopyToState cstate); static void CopySendTextLikeEndOfRow(CopyToState cstate); static void CopySendInt32(CopyToState cstate, int32 val); static void CopySendInt16(CopyToState cstate, int16 val); @@ -349,6 +350,8 @@ CopyToJsonEnd(CopyToState cstate) { if (cstate->opts.force_array) { + if (cstate->json_row_delim_needed) + CopySendTextLikeLineTerminator(cstate); CopySendChar(cstate, ']'); CopySendTextLikeEndOfRow(cstate); } @@ -418,7 +421,11 @@ CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot) if (cstate->opts.force_array) { if (cstate->json_row_delim_needed) + { CopySendChar(cstate, ','); + CopySendTextLikeLineTerminator(cstate); + CopySendChar(cstate, ' '); + } else { /* first row needs no delimiter */ @@ -429,7 +436,10 @@ CopyToJsonOneRow(CopyToState cstate, TupleTableSlot *slot) CopySendData(cstate, cstate->json_buf->data, cstate->json_buf->len); - CopySendTextLikeEndOfRow(cstate); + if (cstate->opts.force_array) + CopySendEndOfRow(cstate); + else + CopySendTextLikeEndOfRow(cstate); } /* @@ -641,11 +651,10 @@ CopySendEndOfRow(CopyToState cstate) } /* - * Wrapper function of CopySendEndOfRow for text, CSV, and json formats. Sends the - * line termination and do common appropriate things for the end of row. + * Append the platform-appropriate line termination for text-like output. */ -static inline void -CopySendTextLikeEndOfRow(CopyToState cstate) +static void +CopySendTextLikeLineTerminator(CopyToState cstate) { switch (cstate->copy_dest) { @@ -664,6 +673,16 @@ CopySendTextLikeEndOfRow(CopyToState cstate) default: break; } +} + +/* + * Wrapper function of CopySendEndOfRow for text, CSV, and json formats. Sends the + * line termination and do common appropriate things for the end of row. + */ +static inline void +CopySendTextLikeEndOfRow(CopyToState cstate) +{ + CopySendTextLikeLineTerminator(cstate); /* Now take the actions related to the end of a row */ CopySendEndOfRow(cstate); diff --git a/src/test/regress/expected/copy.out b/src/test/regress/expected/copy.out index 1714faab39c..3da23de8551 100644 --- a/src/test/regress/expected/copy.out +++ b/src/test/regress/expected/copy.out @@ -85,13 +85,13 @@ copy (values (1), (2)) TO stdout with (format json); {"column1":2} copy (select 1 union all select 2) to stdout with (format json, force_array true); [ - {"?column?":1} -,{"?column?":2} + {"?column?":1}, + {"?column?":2} ] copy (values (1), (2)) TO stdout with (format json, force_array true); [ - {"column1":1} -,{"column1":2} + {"column1":1}, + {"column1":2} ] copy copytest to stdout json; {"style":"DOS","test":"abc\r\ndef","filler":1} @@ -150,17 +150,17 @@ ERROR: COPY FORCE_ARRAY can only be used with JSON mode -- force_array variants copy copytest to stdout (format json, force_array); [ - {"style":"DOS","test":"abc\r\ndef","filler":1} -,{"style":"Unix","test":"abc\ndef","filler":2} -,{"style":"Mac","test":"abc\rdef","filler":3} -,{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4} + {"style":"DOS","test":"abc\r\ndef","filler":1}, + {"style":"Unix","test":"abc\ndef","filler":2}, + {"style":"Mac","test":"abc\rdef","filler":3}, + {"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb","filler":4} ] copy copytest(style, test) to stdout (format json, force_array true); [ - {"style":"DOS","test":"abc\r\ndef"} -,{"style":"Unix","test":"abc\ndef"} -,{"style":"Mac","test":"abc\rdef"} -,{"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb"} + {"style":"DOS","test":"abc\r\ndef"}, + {"style":"Unix","test":"abc\ndef"}, + {"style":"Mac","test":"abc\rdef"}, + {"style":"esc\\ape","test":"a\\r\\\r\\\n\\nb"} ] copy copytest to stdout (format json, force_array false); {"style":"DOS","test":"abc\r\ndef","filler":1} -- 2.50.1 (Apple Git-155)