SQL style guide

Beginner’s Version of This Guide / Quick Start

Overview

These are guidelines to help you write SQL queries that will be easier to read.

Remember that even if you hate a given style at first, generally speaking it is far more important that we have any agreed upon style than that we all like it, and furthermore the odds are that you will eventually learn to like it once you start to follow it.

Queries submitted to the Data teams should follow the style guide, and queries starkly contrasting to, or ignorant of, these guidelines may be asked to be reformatted and resubmitted. Feel free to ask about style rationale, or pose a question how you can make your query (or often taking a step back, question) adhere.

Original SQL style guide by Simon Holywell is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License. Based on a work at http://www.sqlstyle.guide.

General

Do

Avoid

Naming conventions

General

SELECT first_name
FROM staff;

Tables

Columns

Aliasing or correlations

SELECT first_name AS fn
FROM staff AS s1
  JOIN students AS s2
    ON s2.mentor_id = s1.staff_num;
SELECT SUM(s.monitor_tally) AS monitor_total
FROM staff AS s;

Stored procedures

Uniform prefixes

Uniform suffixes

The following suffixes have a universal meaning ensuring the columns can be read and understood easily from SQL code. Use the correct suffix where appropriate.

Query syntax

Reserved words

Always use uppercase for the reserved keywords like SELECT and WHERE.

It is best to avoid the abbreviated keywords and use the full length ones where available (prefer ABSOLUTE to ABS).

Do not use database server specific keywords where an ANSI SQL keyword already exists performing the same function. This helps to make code more portable.

SELECT model_num
FROM phones AS p
WHERE p.release_date > '2014-09-30';

White space

To make the code easier to read it is important that the correct amount of spacing is used. Do not crowd code or remove natural language spaces.

Indentation

To ensure that SQL is readable it is important that standards of indentation are followed.

ONLY the fundamental keywords - SELECT, FROM, WHERE, GROUP BY, HAVING, LIMIT, and ORDER BYshould be fully left justified.

For single SELECTs, you can use the single line form:

SELECT first_name
FROM rappers

If you are SELECTing more than one column, place all selects on their own line indented 2 spaces in a block after the SELECT keyword.

SELECT
  first_name,
  last_name,
  is_still_tippin_on_four_fours,
  is_still_wrapped_in_four_vogues
FROM rappers
WHERE first_name = 'Mike'
  AND last_name = 'Jones'

This allows the reader to quickly scan for the important building blocks of the query.

Spaces

Always include spaces:

SELECT
  a.title,
  a.release_date,
  a.recording_date
FROM albums AS a
WHERE a.title = 'Charcoal Lane'
   OR a.title = 'The New Danger';

Line spacing

Always include newlines/vertical space:

Keeping all the dependent keywords (e.g. ON depends on JOIN, AND depends on WHERE, SET depends on UPDATE right aligned with the top level keywords helps make it clear all the lines are part of the same clause.

INSERT INTO albums (title, release_date, recording_date)
VALUES ('Charcoal Lane', '1990-01-01 01:01:01.00000', '1990-01-01 01:01:01.00000'),
       ('The New Danger', '2008-01-01 01:01:01.00000', '1990-01-01 01:01:01.00000');
UPDATE albums
   SET release_date = '1990-01-01 01:01:01.00000'
WHERE title = 'The New Danger';
SELECT
  a.title,
  a.release_date,
  a.recording_date,
  a.production_date
FROM albums AS a
WHERE a.title = 'Charcoal Lane'
   OR a.title = 'The New Danger';

JOINs

Joins should be indented 2 spaces right from the FROM keyword

Single line JOINs are fine for simple situations

SELECT r.last_name
FROM riders AS r
  INNER JOIN bikes AS b ON r.bike_vin_num = b.vin_num
  INNER JOIN crew AS c ON r.crew_chief_last_name = c.last_name

Multi line JOINs should be indented as per the dependent keywords rule:

SELECT r.last_name
FROM riders AS r
  INNER JOIN bikes AS b
          ON r.bike_vin_num = b.vin_num
         AND r.bike_lane = r.lane
  INNER JOIN crew c ON r.crew_chief_last_name = c.last_name
WHERE id = 5

Boolean Expressions

Complicated boolean expressions can be extremely hard to read. To help with this, left justify boolean subclauses such that the whitespace indicates the current block and the boolean AND/OR are justified the same as the expressions they apply to.

SELECT first_name
FROM rappers
WHERE
  (
    first_name = 'Mike'
    AND
    last_name = 'Jones'
  )
  OR
  (
    was_tipping = 1
    AND
    is_still_tippin_on_four_fours = 1
    AND
    (
      is_still_wrapped_in_four_vogues = 1
      OR
      is_wood_grain_gripping = 0
    )
  )

WITH statements (PostgreSQL only)

Indent them until the closing parentheses.

WITH my_tmp_table AS (
  SELECT r.last_name
  FROM riders AS r
    INNER JOIN bikes AS b ON r.bike_vin_num = b.vin_num
  WHERE id = 10
),

my_other_tmp_table AS (
  SELECT last_name
  FROM staff
)

SELECT *
FROM my_tmp_table
  JOIN my_other_tmp_table ON my_other_tmp_table.last_name = my_tmp_table.last_name

Sub-queries

In PostgreSQL you should probably be writing subqueries with WITH clauses and mostly avoiding the use of inline subqueries.

In MySQL or other query engines that do not support WITH, sub-queries should be left aligned 2 spaces to the right of the opening parentheses and then laid out using the same style as a WITH statement w/r/t parentheses.

SELECT
  r.last_name,
  (
    SELECT MAX(YEAR(championship_date))
    FROM champions AS c
    WHERE c.last_name = r.last_name
      AND c.confirmed = 'Y'
  ) AS last_championship_year
FROM riders AS r
WHERE r.last_name IN
  (
    SELECT c.last_name
    FROM champions AS c
    WHERE YEAR(championship_date) > '2008'
      AND c.confirmed = 'Y'
  )

Case statements (PostreSQL)

CASE and END can either be inline if they are less than 80 characters:

SELECT CASE WHEN x > y THEN 1 ELSE 0 END
FROM table

Or WHEN/END should have 2 space left justification, and WHEN/THEN should be indented the same as the ELSE/value. Multiple AND or OR clauses can be inlined if < 80 characters, or should be right aligned with the whitespace river after WHEN if they are longer

SELECT
  CASE
    WHEN x > y AND x < z
      THEN 'x more than y but less than z'
    WHEN x > y AND x > z
      THEN 'x more than y and more than z'
    WHEN some_very_long_thing_happened BETWEEN '2016-01-01' AND '2016-01-01'
     AND some_event_very_much_longer_thing_happened BETWEEN '2016-01-01' AND '2016-01-01'
      THEN 'something happened later'
    WHEN some_very_long_thing_happened BETWEEN '2016-01-01' AND '2016-01-01'
      OR some_event_very_much_longer_thing_happened BETWEEN '2016-01-01' AND '2016-01-01'
      THEN 'something else'
    ELSE
      'x and y not related'
    END AS city,
  street_address,
  phone_number
FROM office_locations

Case statements (MySql)

SELECT
  CASE postcode
    WHEN 'BN1'
      THEN 'Brighton'
    WHEN 'EH1'
      THEN 'Edinburgh'
    END AS city,
  street_address,
  phone_number
FROM office_locations

Preferred formalisms

SELECT
  CASE postcode
    WHEN 'BN1'
      THEN 'Brighton'
    WHEN 'EH1'
      THEN 'Edinburgh'
    END AS city
FROM office_locations
WHERE country = 'United Kingdom'
  AND opening_time BETWEEN 8 AND 9
  AND postcode IN ('EH1', 'BN1', 'NN1', 'KW1')

Create syntax

When declaring schema information it is also important to maintain human readable code. To facilitate this ensure the column definitions are ordered and grouped where it makes sense to do so.

Indent column definitions by four (4) spaces within the CREATE definition.

Choosing data types

Specifying default values

Constraints and keys

Constraints and their subset, keys, are a very important component of any database definition. They can quickly become very difficult to read and reason about though so it is important that a standard set of guidelines are followed.

Choosing keys

Deciding the column(s) that will form the keys in the definition should be a carefully considered activity as it will effect performance and data integrity.

  1. The key should be unique to some degree.
  2. Consistency in terms of data type for the value across the schema and a lower likelihood of this changing in the future.
  3. Can the value be validated against a standard format (such as one published by ISO)? Encouraging conformity to point 2.
  4. Keeping the key as simple as possible whilst not being scared to use compound keys where necessary.

It is a reasoned and considered balancing act to be performed at the definition of a database. Should requirements evolve in the future it is possible to make changes to the definitions to keep them up to date.

Defining constraints

Once the keys are decided it is possible to define them in the system using constraints along with field value validation.

General
Layout and order
Validation
Example
CREATE TABLE staff (
    PRIMARY KEY (staff_num),
    staff_num      INT(5)       NOT NULL,
    first_name     VARCHAR(100) NOT NULL,
    pens_in_drawer INT(2)       NOT NULL,
                   CONSTRAINT pens_in_drawer_range
                   CHECK(pens_in_drawer >= 1 AND pens_in_drawer < 100)
);

Designs to avoid

Appendix

Reserved keyword reference

A list of ANSI SQL (92, 99 and 2003), MySQL 3 to 5.x, PostgreSQL 8.1, MS SQL Server 2000, MS ODBC and Oracle 10.2 reserved keywords.

A
ABORT
ABS
ABSOLUTE
ACCESS
ACTION
ADA
ADD
ADMIN
AFTER
AGGREGATE
ALIAS
ALL
ALLOCATE
ALSO
ALTER
ALWAYS
ANALYSE
ANALYZE
AND
ANY
ARE
ARRAY
AS
ASC
ASENSITIVE
ASSERTION
ASSIGNMENT
ASYMMETRIC
AT
ATOMIC
ATTRIBUTE
ATTRIBUTES
AUDIT
AUTHORIZATION
AUTO_INCREMENT
AVG
AVG_ROW_LENGTH
BACKUP
BACKWARD
BEFORE
BEGIN
BERNOULLI
BETWEEN
BIGINT
BINARY
BIT
BIT_LENGTH
BITVAR
BLOB
BOOL
BOOLEAN
BOTH
BREADTH
BREAK
BROWSE
BULK
BY
C
CACHE
CALL
CALLED
CARDINALITY
CASCADE
CASCADED
CASE
CAST
CATALOG
CATALOG_NAME
CEIL
CEILING
CHAIN
CHANGE
CHAR
CHAR_LENGTH
CHARACTER
CHARACTER_LENGTH
CHARACTER_SET_CATALOG
CHARACTER_SET_NAME
CHARACTER_SET_SCHEMA
CHARACTERISTICS
CHARACTERS
CHECK
CHECKED
CHECKPOINT
CHECKSUM
CLASS
CLASS_ORIGIN
CLOB
CLOSE
CLUSTER
CLUSTERED
COALESCE
COBOL
COLLATE
COLLATION
COLLATION_CATALOG
COLLATION_NAME
COLLATION_SCHEMA
COLLECT
COLUMN
COLUMN_NAME
COLUMNS
COMMAND_FUNCTION
COMMAND_FUNCTION_CODE
COMMENT
COMMIT
COMMITTED
COMPLETION
COMPRESS
COMPUTE
CONDITION
CONDITION_NUMBER
CONNECT
CONNECTION
CONNECTION_NAME
CONSTRAINT
CONSTRAINT_CATALOG
CONSTRAINT_NAME
CONSTRAINT_SCHEMA
CONSTRAINTS
CONSTRUCTOR
CONTAINS
CONTAINSTABLE
CONTINUE
CONVERSION
CONVERT
COPY
CORR
CORRESPONDING
COUNT
COVAR_POP
COVAR_SAMP
CREATE
CREATEDB
CREATEROLE
CREATEUSER
CROSS
CSV
CUBE
CUME_DIST
CURRENT
CURRENT_DATE
CURRENT_DEFAULT_TRANSFORM_GROUP
CURRENT_PATH
CURRENT_ROLE
CURRENT_TIME
CURRENT_TIMESTAMP
CURRENT_TRANSFORM_GROUP_FOR_TYPE
CURRENT_USER
CURSOR
CURSOR_NAME
CYCLE
DATA
DATABASE
DATABASES
DATE
DATETIME
DATETIME_INTERVAL_CODE
DATETIME_INTERVAL_PRECISION
DAY
DAY_HOUR
DAY_MICROSECOND
DAY_MINUTE
DAY_SECOND
DAYOFMONTH
DAYOFWEEK
DAYOFYEAR
DBCC
DEALLOCATE
DEC
DECIMAL
DECLARE
DEFAULT
DEFAULTS
DEFERRABLE
DEFERRED
DEFINED
DEFINER
DEGREE
DELAY_KEY_WRITE
DELAYED
DELETE
DELIMITER
DELIMITERS
DENSE_RANK
DENY
DEPTH
DEREF
DERIVED
DESC
DESCRIBE
DESCRIPTOR
DESTROY
DESTRUCTOR
DETERMINISTIC
DIAGNOSTICS
DICTIONARY
DISABLE
DISCONNECT
DISK
DISPATCH
DISTINCT
DISTINCTROW
DISTRIBUTED
DIV
DO
DOMAIN
DOUBLE
DROP
DUAL
DUMMY
DUMP
DYNAMIC
DYNAMIC_FUNCTION
DYNAMIC_FUNCTION_CODE
EACH
ELEMENT
ELSE
ELSEIF
ENABLE
ENCLOSED
ENCODING
ENCRYPTED
END
END-EXEC
ENUM
EQUALS
ERRLVL
ESCAPE
ESCAPED
EVERY
EXCEPT
EXCEPTION
EXCLUDE
EXCLUDING
EXCLUSIVE
EXEC
EXECUTE
EXISTING
EXISTS
EXIT
EXP
EXPLAIN
EXTERNAL
EXTRACT
FALSE
FETCH
FIELDS
FILE
FILLFACTOR
FILTER
FINAL
FIRST
FLOAT
FLOAT4
FLOAT8
FLOOR
FLUSH
FOLLOWING
FOR
FORCE
FOREIGN
FORTRAN
FORWARD
FOUND
FREE
FREETEXT
FREETEXTTABLE
FREEZE
FROM
FULL
FULLTEXT
FUNCTION
FUSION
G
GENERAL
GENERATED
GET
GLOBAL
GO
GOTO
GRANT
GRANTED
GRANTS
GREATEST
GROUP
GROUPING
HANDLER
HAVING
HEADER
HEAP
HIERARCHY
HIGH_PRIORITY
HOLD
HOLDLOCK
HOST
HOSTS
HOUR
HOUR_MICROSECOND
HOUR_MINUTE
HOUR_SECOND
IDENTIFIED
IDENTITY
IDENTITY_INSERT
IDENTITYCOL
IF
IGNORE
ILIKE
IMMEDIATE
IMMUTABLE
IMPLEMENTATION
IMPLICIT
IN
INCLUDE
INCLUDING
INCREMENT
INDEX
INDICATOR
INFILE
INFIX
INHERIT
INHERITS
INITIAL
INITIALIZE
INITIALLY
INNER
INOUT
INPUT
INSENSITIVE
INSERT
INSERT_ID
INSTANCE
INSTANTIABLE
INSTEAD
INT
INT1
INT2
INT3
INT4
INT8
INTEGER
INTERSECT
INTERSECTION
INTERVAL
INTO
INVOKER
IS
ISAM
ISNULL
ISOLATION
ITERATE
JOIN
K
KEY
KEY_MEMBER
KEY_TYPE
KEYS
KILL
LANCOMPILER
LANGUAGE
LARGE
LAST
LAST_INSERT_ID
LATERAL
LEADING
LEAST
LEAVE
LEFT
LENGTH
LESS
LEVEL
LIKE
LIMIT
LINENO
LINES
LISTEN
LN
LOAD
LOCAL
LOCALTIME
LOCALTIMESTAMP
LOCATION
LOCATOR
LOCK
LOGIN
LOGS
LONG
LONGBLOB
LONGTEXT
LOOP
LOW_PRIORITY
LOWER
M
MAP
MATCH
MATCHED
MAX
MAX_ROWS
MAXEXTENTS
MAXVALUE
MEDIUMBLOB
MEDIUMINT
MEDIUMTEXT
MEMBER
MERGE
MESSAGE_LENGTH
MESSAGE_OCTET_LENGTH
MESSAGE_TEXT
METHOD
MIDDLEINT
MIN
MIN_ROWS
MINUS
MINUTE
MINUTE_MICROSECOND
MINUTE_SECOND
MINVALUE
MLSLABEL
MOD
MODE
MODIFIES
MODIFY
MODULE
MONTH
MONTHNAME
MORE
MOVE
MULTISET
MUMPS
MYISAM
NAME
NAMES
NATIONAL
NATURAL
NCHAR
NCLOB
NESTING
NEW
NEXT
NO
NO_WRITE_TO_BINLOG
NOAUDIT
NOCHECK
NOCOMPRESS
NOCREATEDB
NOCREATEROLE
NOCREATEUSER
NOINHERIT
NOLOGIN
NONCLUSTERED
NONE
NORMALIZE
NORMALIZED
NOSUPERUSER
NOT
NOTHING
NOTIFY
NOTNULL
NOWAIT
NULL
NULLABLE
NULLIF
NULLS
NUMBER
NUMERIC
OBJECT
OCTET_LENGTH
OCTETS
OF
OFF
OFFLINE
OFFSET
OFFSETS
OIDS
OLD
ON
ONLINE
ONLY
OPEN
OPENDATASOURCE
OPENQUERY
OPENROWSET
OPENXML
OPERATION
OPERATOR
OPTIMIZE
OPTION
OPTIONALLY
OPTIONS
OR
ORDER
ORDERING
ORDINALITY
OTHERS
OUT
OUTER
OUTFILE
OUTPUT
OVER
OVERLAPS
OVERLAY
OVERRIDING
OWNER
PACK_KEYS
PAD
PARAMETER
PARAMETER_MODE
PARAMETER_NAME
PARAMETER_ORDINAL_POSITION
PARAMETER_SPECIFIC_CATALOG
PARAMETER_SPECIFIC_NAME
PARAMETER_SPECIFIC_SCHEMA
PARAMETERS
PARTIAL
PARTITION
PASCAL
PASSWORD
PATH
PCTFREE
PERCENT
PERCENT_RANK
PERCENTILE_CONT
PERCENTILE_DISC
PLACING
PLAN
PLI
POSITION
POSTFIX
POWER
PRECEDING
PRECISION
PREFIX
PREORDER
PREPARE
PREPARED
PRESERVE
PRIMARY
PRINT
PRIOR
PRIVILEGES
PROC
PROCEDURAL
PROCEDURE
PROCESS
PROCESSLIST
PUBLIC
PURGE
QUOTE
RAID0
RAISERROR
RANGE
RANK
RAW
READ
READS
READTEXT
REAL
RECHECK
RECONFIGURE
RECURSIVE
REF
REFERENCES
REFERENCING
REGEXP
REGR_AVGX
REGR_AVGY
REGR_COUNT
REGR_INTERCEPT
REGR_R2
REGR_SLOPE
REGR_SXX
REGR_SXY
REGR_SYY
REINDEX
RELATIVE
RELEASE
RELOAD
RENAME
REPEAT
REPEATABLE
REPLACE
REPLICATION
REQUIRE
RESET
RESIGNAL
RESOURCE
RESTART
RESTORE
RESTRICT
RESULT
RETURN
RETURNED_CARDINALITY
RETURNED_LENGTH
RETURNED_OCTET_LENGTH
RETURNED_SQLSTATE
RETURNS
REVOKE
RIGHT
RLIKE
ROLE
ROLLBACK
ROLLUP
ROUTINE
ROUTINE_CATALOG
ROUTINE_NAME
ROUTINE_SCHEMA
ROW
ROW_COUNT
ROW_NUMBER
ROWCOUNT
ROWGUIDCOL
ROWID
ROWNUM
ROWS
RULE
SAVE
SAVEPOINT
SCALE
SCHEMA
SCHEMA_NAME
SCHEMAS
SCOPE
SCOPE_CATALOG
SCOPE_NAME
SCOPE_SCHEMA
SCROLL
SEARCH
SECOND
SECOND_MICROSECOND
SECTION
SECURITY
SELECT
SELF
SENSITIVE
SEPARATOR
SEQUENCE
SERIALIZABLE
SERVER_NAME
SESSION
SESSION_USER
SET
SETOF
SETS
SETUSER
SHARE
SHOW
SHUTDOWN
SIGNAL
SIMILAR
SIMPLE
SIZE
SMALLINT
SOME
SONAME
SOURCE
SPACE
SPATIAL
SPECIFIC
SPECIFIC_NAME
SPECIFICTYPE
SQL
SQL_BIG_RESULT
SQL_BIG_SELECTS
SQL_BIG_TABLES
SQL_CALC_FOUND_ROWS
SQL_LOG_OFF
SQL_LOG_UPDATE
SQL_LOW_PRIORITY_UPDATES
SQL_SELECT_LIMIT
SQL_SMALL_RESULT
SQL_WARNINGS
SQLCA
SQLCODE
SQLERROR
SQLEXCEPTION
SQLSTATE
SQLWARNING
SQRT
SSL
STABLE
START
STARTING
STATE
STATEMENT
STATIC
STATISTICS
STATUS
STDDEV_POP
STDDEV_SAMP
STDIN
STDOUT
STORAGE
STRAIGHT_JOIN
STRICT
STRING
STRUCTURE
STYLE
SUBCLASS_ORIGIN
SUBLIST
SUBMULTISET
SUBSTRING
SUCCESSFUL
SUM
SUPERUSER
SYMMETRIC
SYNONYM
SYSDATE
SYSID
SYSTEM
SYSTEM_USER
TABLE
TABLE_NAME
TABLES
TABLESAMPLE
TABLESPACE
TEMP
TEMPLATE
TEMPORARY
TERMINATE
TERMINATED
TEXT
TEXTSIZE
THAN
THEN
TIES
TIME
TIMESTAMP
TIMEZONE_HOUR
TIMEZONE_MINUTE
TINYBLOB
TINYINT
TINYTEXT
TO
TOAST
TOP
TOP_LEVEL_COUNT
TRAILING
TRAN
TRANSACTION
TRANSACTION_ACTIVE
TRANSACTIONS_COMMITTED
TRANSACTIONS_ROLLED_BACK
TRANSFORM
TRANSFORMS
TRANSLATE
TRANSLATION
TREAT
TRIGGER
TRIGGER_CATALOG
TRIGGER_NAME
TRIGGER_SCHEMA
TRIM
TRUE
TRUNCATE
TRUSTED
TSEQUAL
TYPE
UESCAPE
UID
UNBOUNDED
UNCOMMITTED
UNDER
UNDO
UNENCRYPTED
UNION
UNIQUE
UNKNOWN
UNLISTEN
UNLOCK
UNNAMED
UNNEST
UNSIGNED
UNTIL
UPDATE
UPDATETEXT
UPPER
USAGE
USE
USER
USER_DEFINED_TYPE_CATALOG
USER_DEFINED_TYPE_CODE
USER_DEFINED_TYPE_NAME
USER_DEFINED_TYPE_SCHEMA
USING
UTC_DATE
UTC_TIME
UTC_TIMESTAMP
VACUUM
VALID
VALIDATE
VALIDATOR
VALUE
VALUES
VAR_POP
VAR_SAMP
VARBINARY
VARCHAR
VARCHAR2
VARCHARACTER
VARIABLE
VARIABLES
VARYING
VERBOSE
VIEW
VOLATILE
WAITFOR
WHEN
WHENEVER
WHERE
WHILE
WIDTH_BUCKET
WINDOW
WITH
WITHIN
WITHOUT
WORK
WRITE
WRITETEXT
X509
XOR
YEAR
YEAR_MONTH
ZEROFILL
ZONE