Document string literal syntax

Author: nene

sql/identifiers.md

@@ -35,12 +35,13 @@ There is a considerable variation in implementations:
 - `".."` [Redshift][]
 - `` `..` `` [Spark][]
 - `".."`, `` `..` ``, `[..]` [SQLite][sqlite-keywords]
-- `".."`, `[..]` [Transact-SQL][]
+- `".."`<sup>3</sup>, `[..]` [Transact-SQL][]
 
 Notes:
 
 1. when ANSI_QUOTES mode enabled
 2. when MSSQL mode enabled
+3. unless QUOTED_IDENTIFIER option has been set OFF
 
 [bigquery]: https://cloud.google.com/bigquery/docs/reference/standard-sql/lexical
 [db2]: https://www.ibm.com/docs/en/db2/9.7?topic=elements-identifiers

sql/strings.md

@@ -0,0 +1,69 @@
+# Strings
+
+SQL standard supports single-quoted strings `'..'` with repeated quote `''` used for escaping.
+The real world implementations have lots of variation:
+
+- [BigQuery][]:
+  - `".."`, `'..'`, `"""..."""`, `'''..'''` (backslash `\` used for escaping)
+  - `R".."`, `r'''..'''` the same as above, but with `r` or `R` prefix (backlashes not used for escaping)
+  - `B".."`, `b'''..'''` the same as above, but with `b` or `B` prefix (backlashes not used for escaping)
+  - `RB".."`, `br'''..'''` the same as above, but with additional `r` or `R` prefix (backlashes not used for escaping)
+- [DB2][]:
+  - `'..'` (two single quotes `''` are used for escaping)
+  - `X'..'` a hex string (no escaping)
+  - `U&'..'` an unicode string (two single quotes `''` are used for escaping)
+  - `G'..'`, `N'..'` a graphic string
+  - `GX'..'` a graphic hex string (no escaping)
+  - `UX'..'` an UCS-2 graphic string (no escaping)
+- [Hive][]: `'..'`, `".."` (backslash `\` used for escaping)
+- [MariaDB][]:
+  - `'..'` (backslash `\`<sup>1</sup> or repeated single-quote `''` used for escaping)
+  - `x'..'`, `X'..'` [hex string][mariadb-hex]
+- [MySQL][]:
+  - `'..'`, `".."`<sup>2</sup> (backslash `\`<sup>1</sup> or repeated quote (`''` or `""`) used for escaping)
+  - `x'..'`, `X'..'` [hex string][mysql-hex]
+- [N1QL][]: `".."` (backslash `\` used for escaping)
+- [PL/SQL][]:
+  - `'..'` (two single quotes `''` are used for escaping)
+  - `N'..'`, `n'..'` a string using a natural character set
+  - `Q'x..x'`, `q'x..x'` where `x` is a custom delimiter character
+  - `q'{..}'`, `q'[..]'`, `q'<..>'`, `q'(..)'` special handling for certain delimiters in above syntax
+- [PostgreSQL][]:
+  - `'..'` (two single quotes `''` are used for escaping)
+  - `E'..'`, `e'..'` string with C-style escapes (backslash `\` or repeated single-quote `''` used for escaping)
+  - `U&'..'`, `u&'..'` string with unicode escapes
+  - `$$..$$`, `$delim$..$delim$` dollar-quoted string with optional custom delimiters
+  - `B'..'`, `b'..'` bit string
+  - `X'..'`, `x'..'` hex string
+- [Redshift][]: `'..'`
+- [Spark][]:
+  - `'..'` (backslash `\` used for escaping)
+  - `X'..'` hex string
+- [SQLite][]:
+  - `'..'` (two single quotes `''` are used for escaping)
+  - `X'..'`, `x'..'` hex string
+- [Transact-SQL][]:
+  - `'..'` (two single quotes `''` are used for escaping)
+  - (`".."`<sup>3</sup>)
+  - `N'..'` (`N".."`<sup>3</sup>) unicode strings
+
+### Notes:
+
+1. unless the SQL_MODE has been set to NO_BACKSLASH_ESCAPES.
+2. unless ANSI_QUOTES mode is enabled.
+3. if the QUOTED_IDENTIFIER option has been set OFF.
+
+[bigquery]: https://cloud.google.com/bigquery/docs/reference/standard-sql/lexical#string_and_bytes_literals
+[db2]: https://www.ibm.com/docs/en/db2/9.7?topic=elements-constants
+[hive]: https://cwiki.apache.org/confluence/display/hive/languagemanual%20types#LanguageManualTypes-StringsstringStrings
+[mariadb]: https://mariadb.com/kb/en/string-literals/
+[mariadb-hex]: https://mariadb.com/kb/en/hexadecimal-literals/
+[mysql]: https://dev.mysql.com/doc/refman/8.0/en/string-literals.html
+[mysql-hex]: https://dev.mysql.com/doc/refman/8.0/en/hexadecimal-literals.html
+[n1ql]: https://docs.couchbase.com/server/current/n1ql/n1ql-language-reference/literals.html#strings
+[pl/sql]: https://docs.oracle.com/cd/B19306_01/server.102/b14200/sql_elements003.htm#i42617
+[postgresql]: https://www.postgresql.org/docs/current/sql-syntax-lexical.html#SQL-SYNTAX-CONSTANTS
+[redshift]: https://docs.aws.amazon.com/redshift/latest/dg/r_Examples_with_character_types.html
+[spark]: https://spark.apache.org/docs/latest/sql-ref-literals.html#string-literal
+[sqlite]: https://www.sqlite.org/lang_expr.html#literal_values_constants_
+[transact-sql]: https://docs.microsoft.com/en-us/sql/t-sql/data-types/constants-transact-sql?view=sql-server-ver15

sql/syntax.md

@@ -4,4 +4,5 @@ Reference of SQL syntax variations.
 
 - [Identifiers](./identifiers.md)
 - [Parameters](./parameters.md)
+- [Strings](./strings.md)
 - [SELECT](./select.md)