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MDEV-39843: Prefix index causes incorrect range query result #5394

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MDEV-39843: Prefix index causes incorrect range query result #5394

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2 changes: 1 addition & 1 deletion mysql-test/main/ctype_utf8.result
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Original file line number Diff line number Diff line change
Expand Up @@ -1521,9 +1521,9 @@ id a b
11 bbbbbb 60
SELECT id, a, b FROM t1 WHERE a BETWEEN 'aaaa' AND 'bbbbbb';
id a b
6 bbbbbb 40
8 aaaa 10
9 aaaa 50
6 bbbbbb 40
11 bbbbbb 60
SELECT id, a FROM t1 WHERE a='bbbbbb';
id a
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2 changes: 1 addition & 1 deletion mysql-test/main/ctype_utf8mb4.result
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Original file line number Diff line number Diff line change
Expand Up @@ -1546,9 +1546,9 @@ id a b
11 bbbbbb 60
SELECT id, a, b FROM t1 WHERE a BETWEEN 'aaaa' AND 'bbbbbb';
id a b
6 bbbbbb 40
8 aaaa 10
9 aaaa 50
6 bbbbbb 40
11 bbbbbb 60
SELECT id, a FROM t1 WHERE a='bbbbbb';
id a
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23 changes: 23 additions & 0 deletions mysql-test/main/range.result
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Original file line number Diff line number Diff line change
Expand Up @@ -3873,3 +3873,26 @@ DROP TABLE lineitem;
#
# End of 11.0 tests
#
#
# MDEV-39843: Prefix index causes incorrect range query result
#
SET NAMES utf8mb4;
CREATE TABLE t0 (c0 LONGTEXT, KEY i0 (c0(1)));
INSERT INTO t0(c0) VALUES ('꙰dcF'), ('kER');
SELECT c0 FROM t0 WHERE 'C0' <= t0.c0;
c0
꙰dcF
kER
explain SELECT c0 FROM t0 WHERE 'C0' <= t0.c0;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t0 ALL i0 NULL NULL NULL 2 Using where
DROP INDEX i0 ON t0;
SELECT c0 FROM t0 WHERE 'C0' <= t0.c0;
c0
꙰dcF
kER
explain SELECT c0 FROM t0 WHERE 'C0' <= t0.c0;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t0 ALL NULL NULL NULL NULL 2 Using where
DROP TABLE t0;
# End of 11.4 tests
21 changes: 21 additions & 0 deletions mysql-test/main/range.test
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Original file line number Diff line number Diff line change
Expand Up @@ -2641,3 +2641,24 @@ DROP TABLE lineitem;
--echo #
--echo # End of 11.0 tests
--echo #

--echo #
--echo # MDEV-39843: Prefix index causes incorrect range query result
--echo #

SET NAMES utf8mb4;

CREATE TABLE t0 (c0 LONGTEXT, KEY i0 (c0(1)));
INSERT INTO t0(c0) VALUES ('꙰dcF'), ('kER');

SELECT c0 FROM t0 WHERE 'C0' <= t0.c0;
explain SELECT c0 FROM t0 WHERE 'C0' <= t0.c0;

DROP INDEX i0 ON t0;

SELECT c0 FROM t0 WHERE 'C0' <= t0.c0;
explain SELECT c0 FROM t0 WHERE 'C0' <= t0.c0;

DROP TABLE t0;

--echo # End of 11.4 tests
27 changes: 27 additions & 0 deletions sql/opt_range.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -9701,6 +9701,25 @@ SEL_ARG *Field::stored_field_make_mm_leaf_bounded_int(RANGE_OPT_PARAM *param,
}


/*
Check whether a partial (prefix) key segment cannot be used as a range
bound because of the collation.

For a collation with a complex, non one-to-one character-to-weight mapping
(contractions, expansions or ignorable characters: MY_CS_NON1TO1) the sort
key of a character prefix does not preserve the ordering of the full value,
so neither a lower nor an upper prefix bound is sound.
Equality is unaffected and keeps using the prefix (the full condition is
always rechecked).
*/
static bool prefix_key_part_unsafe_for_range(const KEY_PART *key_part,
const Field *field)
{
return (key_part->flag & HA_PART_KEY_SEG) &&
(field->charset()->state & MY_CS_NON1TO1);
}


SEL_ARG *Field::stored_field_make_mm_leaf(RANGE_OPT_PARAM *param,
KEY_PART *key_part,
scalar_comparison_op op,
Expand All @@ -9715,12 +9734,20 @@ SEL_ARG *Field::stored_field_make_mm_leaf(RANGE_OPT_PARAM *param,

switch (op) {
case SCALAR_CMP_LE:
if (prefix_key_part_unsafe_for_range(key_part, this))
DBUG_RETURN(0);
DBUG_RETURN(new (mem_root) SEL_ARG_LE(str, this));
case SCALAR_CMP_LT:
if (prefix_key_part_unsafe_for_range(key_part, this))
DBUG_RETURN(0);
DBUG_RETURN(new (mem_root) SEL_ARG_LT(thd, str, key_part, this, value));
case SCALAR_CMP_GT:
if (prefix_key_part_unsafe_for_range(key_part, this))
DBUG_RETURN(0);
DBUG_RETURN(new (mem_root) SEL_ARG_GT(thd, str, key_part, this, value));
case SCALAR_CMP_GE:
if (prefix_key_part_unsafe_for_range(key_part, this))
DBUG_RETURN(0);
DBUG_RETURN(new (mem_root) SEL_ARG_GE(thd, str, key_part, this, value));
Comment on lines 9735 to 9751

@gemini-code-assist gemini-code-assist Bot Jul 16, 2026

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medium

The check prefix_key_part_unsafe_for_range(key_part, this) is duplicated across all four inequality comparison cases (SCALAR_CMP_LE, SCALAR_CMP_LT, SCALAR_CMP_GT, SCALAR_CMP_GE). Consolidating this check before the switch statement reduces code duplication and improves maintainability.

  if ((op == SCALAR_CMP_LE || op == SCALAR_CMP_LT ||
       op == SCALAR_CMP_GT || op == SCALAR_CMP_GE) &&
      prefix_key_part_unsafe_for_range(key_part, this))
    DBUG_RETURN(0);

  switch (op) {
  case SCALAR_CMP_LE:
    DBUG_RETURN(new (mem_root) SEL_ARG_LE(str, this));
  case SCALAR_CMP_LT:
    DBUG_RETURN(new (mem_root) SEL_ARG_LT(thd, str, key_part, this, value));
  case SCALAR_CMP_GT:
    DBUG_RETURN(new (mem_root) SEL_ARG_GT(thd, str, key_part, this, value));
  case SCALAR_CMP_GE:
    DBUG_RETURN(new (mem_root) SEL_ARG_GE(thd, str, key_part, this, value));

case SCALAR_CMP_EQ:
case SCALAR_CMP_EQUAL:
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