[#MDEV-27544] database() function under UNION ALL truncates results to 34 characters despite databases having up to 64 character names

$ db=$(printf 'a%.0s' {1..40})

$ echo $db

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

$ podman run -d --rm -e MYSQL_ALLOW_EMPTY_PASSWORD=1 -e MYSQL_DATABASE=$db -e MYSQL_USER=u -e MYSQL_PASSWORD=p --name m55 mariadb:5.5

1b2c0740bf664b8a3da8071bb96234a86fe8dd5f3eb6348598f5d0c2b59ede56

$ podman exec -ti m55 mysql -u u -pp  --column-type-info -e 'select database() as "database" union all select database()' $db

Field   1:  `database`

Catalog:    `def`

Database:   ``

Table:      ``

Org_table:  ``

Type:       VAR_STRING

Collation:  latin1_swedish_ci (8)

Length:     34

Max_length: 34

Decimals:   0

Flags:

+------------------------------------+

| database                           |

+------------------------------------+

| aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa |

| aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa |

+------------------------------------+

$ podman exec -ti m55 mysql -u u -pp  --column-type-info -e 'select database()' $db

Field   1:  `database()`

Catalog:    `def`

Database:   ``

Table:      ``

Org_table:  ``

Type:       VAR_STRING

Collation:  latin1_swedish_ci (8)

Length:     34

Max_length: 40

Decimals:   31

Flags:

+------------------------------------------+

| database()                               |

+------------------------------------------+

| aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa |

+------------------------------------------+

diff --git a/sql/item_strfunc.h b/sql/item_strfunc.h

index 0bf21b63ac9..3abc7fba2f6 100644

--- a/sql/item_strfunc.h

+++ b/sql/item_strfunc.h

@@ -717,7 +717,7 @@ class Item_func_database :public Item_func_sysconst

   String *val_str(String *);

   bool fix_length_and_dec()

-    max_length= MAX_FIELD_NAME * system_charset_info->mbmaxlen;

+    max_length= NAME_LEN;

     maybe_null=1;

     return FALSE;

$ mc -u root --default-character-set=utf8mb4 -e "create database $db"; mc -u root --default-character-set=utf8mb4   --column-type-info -e 'select database() as "database" union all select database()' $db

Field   1:  `database`

Catalog:    `def`

Database:   ``

Table:      ``

Org_table:  ``

Type:       VAR_STRING

Collation:  utf8mb4_general_ci (45)

Length:     256

Max_length: 40

Decimals:   39

Flags:

+------------------------------------------+

| database                                 |

+------------------------------------------+

| aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa |

| aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa |

+------------------------------------------+

~/repos/build-mariadb-server-10.2

$ wc -c

aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa40

~/repos/build-mariadb-server-10.2

$ mc -u root --default-character-set=latin1   --column-type-info -e 'select database() as "database" union all select database()' $db

Field   1:  `database`

Catalog:    `def`

Database:   ``

Table:      ``

Org_table:  ``

Type:       VAR_STRING

Collation:  latin1_swedish_ci (8)

Length:     64

Max_length: 40

Decimals:   39

Flags:

+------------------------------------------+

| database                                 |

+------------------------------------------+

| aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa |

| aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa |

+------------------------------------------+

   bool fix_length_and_dec()

     max_length= NAME_CHAR_LEN * system_charset_info->mbmaxlen;

     maybe_null=1;

     return FALSE;

[MDEV-27544] database() function under UNION ALL truncates results to 34 characters despite databases having up to 64 character names Created: 2022-01-19 Updated: 2022-01-20 Resolved: 2022-01-20
Status:	Closed
Project:	MariaDB Server
Component/s:	Data types
Affects Version/s:	5.5.68, 10.7.1
Fix Version/s:	10.2.42, 10.3.33, 10.4.23, 10.5.14, 10.6.6, 10.7.2

[MDEV-27544] database() function under UNION ALL truncates results to 34 characters despite databases having up to 64 character names Created: 2022-01-19 Updated: 2022-01-20 Resolved: 2022-01-20