Getting Started with HoneySQL

HoneySQL lets you build complex SQL statements by constructing and composing Clojure data structures and then formatting that data to a SQL statement (string) and any parameters it needs.

Installation

For the Clojure CLI, add the following dependency to your deps.edn file:

    com.github.seancorfield/honeysql {:mvn/version "2.4.1002"}

For Leiningen, add the following dependency to your project.clj file:

    [com.github.seancorfield/honeysql "2.4.1002"]

HoneySQL produces SQL statements but does not execute them. To execute SQL statements, you will also need a JDBC wrapper like seancorfield/next.jdbc and a JDBC driver for the database you use.

You can also experiment with HoneySQL directly in a browser -- no installation required -- using John Shaffer's awesome HoneySQL web app, written in ClojureScript!

Basic Concepts

SQL statements are represented as hash maps, with keys that represent clauses in SQL. SQL expressions are generally represented as sequences, where the first element identifies the function or operator and the remaining elements are the arguments or operands.

honey.sql/format takes a hash map representing a SQL statement and produces a vector, suitable for use with next.jdbc or clojure.java.jdbc, that has the generated SQL string as the first element followed by any parameter values identified in the SQL expressions:

(require '[honey.sql :as sql])

(sql/format {:select [:*], :from [:table], :where [:= :id 1]})
;;=> ["SELECT * FROM table WHERE id = ?" 1]

By default, any values found in the data structure, that are not keywords or symbols, are treated as positional parameters and replaced by ? in the SQL string and lifted out into the vector that is returned from format.

Most clauses expect a sequence as their value, containing either a list of SQL entities or the representation of a SQL expression. Some clauses accept a single SQL entity. A few accept a more specialized form (such as :set accepting a hash map of SQL entities and SQL expressions).

A SQL entity can be a simple keyword (or symbol) or a pair that represents a SQL entity and its alias (where aliases are allowed):

(sql/format {:select [:t.id [:name :item]], :from [[:table :t]], :where [:= :id 1]})
;;=> ["SELECT t.id, name AS item FROM table AS t WHERE id = ?" 1]

The FROM clause now has a pair that identifies the SQL entity table and its alias t. Columns can be identified either by their qualified name (as in :t.id) or their unqualified name (as in :name). The SELECT clause here identifies two SQL entities: t.id and name with the latter aliased to item.

Symbols can also be used, but you need to quote them to avoid evaluation:

(sql/format '{select [t.id [name item]], from [[table t]], where [= id 1]})
;;=> ["SELECT t.id, name AS item FROM table AS t WHERE id = ?" 1]

;; or you can use (..) instead of [..] when quoted to produce the same result:
(sql/format '{select (t.id (name item)), from ((table t)), where (= id 1)})
;;=> ["SELECT t.id, name AS item FROM table AS t WHERE id = ?" 1]

If you wish, you can specify SQL entities as namespace-qualified keywords (or symbols) and the namespace portion will treated as the table name, i.e., :foo/bar instead of :foo.bar:

;; notice the following both produce the same result:
(sql/format {:select [:t/id [:name :item]], :from [[:table :t]], :where [:= :id 1]})
;;=> ["SELECT t.id, name AS item FROM table AS t WHERE id = ?" 1]
(sql/format '{select [t/id [name item]], from [[table t]], where [= id 1]})
;;=> ["SELECT t.id, name AS item FROM table AS t WHERE id = ?" 1]

SQL Expressions

In addition to using hash maps to describe SQL clauses, HoneySQL uses sequences to describe SQL expressions. Any sequence that begins with a keyword (or symbol) is considered to be a kind of function invocation. Certain "functions" are considered to be "special syntax" and have custom rendering. Some "functions" are considered to be operators. In general, [:foo :a 42 "c"] will render as FOO(a, ?, ?) with the parameters 42 and "c" lifted out into the overall vector result (with a SQL string followed by all its parameters).

Note: you can use the :numbered true option to format to produce SQL containing numbered placeholders, like FOO(a, $1, $2), instead of positional placeholders (?).

As of 2.4.1002, function calls with "named" arguments are supported which some databases support, e.g., MySQL and PostgreSQL both have SUBSTRING():

[:substring :col 3 4]              ;=> SUBSTRING(col, 3, 4)
;; can also be written:
[:substring :col :!from 3 :!for 4] ;=> SUBSTRING(col FROM 3 FOR 4)

In a function call, any keywords (or symbols) that begin with ! followed by a letter are treated as inline SQL keywords to be used instead of , between arguments -- or in front of arguments, such as for TRIM():

[:trim :!leading "x" :!from :col] ;=> TRIM(LEADING ? FROM col), with "x" parameter
[:trim :!both :!from :col]        ;=> TRIM(BOTH FROM col), trims spaces
;; adjacent inline SQL keywords can be combined with a hyphen:
[:trim :!both-from :col]          ;=> TRIM(BOTH FROM col)
;; (because - in a SQL keyword is replaced by a space)

Operators are all treated as variadic (except for := and :<> / :!= / :not= which are binary and require exactly two operands). Special syntax can have zero or more arguments and each form is described in the Special Syntax section.

Some examples:

[:= :a 42]                              ;=> "a = ?" with a parameter of 42
[:+ 42 :a :b]                           ;=> "? + a + b" with a parameter of 42
[:= :x [:inline "foo"]]                 ;=> "x = 'foo'" -- the string is inlined
[:now]                                  ;=> "NOW()"
[:count :*]                             ;=> "COUNT(*)"
[:or [:<> :name nil] [:= :status-id 0]] ;=> "(name IS NOT NULL) OR (status_id = ?)"
;; with a parameter of 0 -- the nil value is inlined as NULL

:inline is an example of "special syntax" and it renders its (single) argument as part of the SQL string generated by format.

Another form of special syntax that is treated as function calls is keywords or symbols that begin with %. Such keywords (or symbols) are split at . and turned into function calls:

%now     ;=> NOW()
%count.* ;=> COUNT(*)
%max.foo ;=> MAX(foo)
%f.a.b   ;=> F(a,b)

If you need to reference a table or alias for a column, you can use qualified names in a function invocation:

%max.foo/bar ;=> MAX(foo.bar)

The latter syntax can be convenient in a SELECT because [:a :b] is otherwise taken as a column and its alias, so selecting a function call expression requires an extra level of nesting:

(sql/format {:select [:a]})
;;=> ["SELECT a"]
(sql/format {:select [[:a :b]]})
;;=> ["SELECT a AS b"]
(sql/format {:select [[[:a :b]]]})
;;=> ["SELECT A(b)"]
;; or use the % notification:
(sql/format {:select [:%a.b]})
;;=> ["SELECT A(b)"]
(sql/format {:select [[[:a :b] :c]]})
;;=> ["SELECT A(b) AS c"]
(sql/format {:select [[:%a.b :c]]})
;;=> ["SELECT A(b) AS c"]
;; putting it all together:
(sql/format {:select [:x [:y :d] [[:z :e]] [[:z :f] :g]]})
;;=> ["SELECT x, y AS d, Z(e), Z(f) AS g"]
(sql/format {:select [:x [:y :d] [:%z.e] [:%z.f :g]]})
;;=> ["SELECT x, y AS d, Z(e), Z(f) AS g"]

SQL Parameters

As indicated in the preceding sections, values found in the DSL data structure that are not keywords or symbols are lifted out as positional parameters. By default, they are replaced by ? in the generated SQL string and added to the parameter list in order:

[:between :size 10 20] ;=> "size BETWEEN ? AND ?" with parameters 10 and 20

If you specify the :numbered true option to format, numbered placeholders ($1, $2, etc) will be used instead of positional placeholders (?).

;; with :numbered true option:
[:between :size 10 20] ;=> "size BETWEEN $1 AND $2" with parameters 10 and 20

HoneySQL also supports named parameters. There are two ways of identifying a named parameter:

• a keyword or symbol that begins with ?
• the :param special (functional) syntax

The values of those parameters are supplied in the format call as the :params key of the options hash map.

(sql/format {:select [:*] :from [:table]
             :where [:= :a :?x]}
            {:params {:x 42}})
;;=> ["SELECT * FROM table WHERE a = ?" 42]
(sql/format {:select [:*] :from [:table]
             :where [:= :a [:param :x]]}
            {:params {:x 42}})
;;=> ["SELECT * FROM table WHERE a = ?" 42]

Or with :numbered true:

(sql/format {:select [:*] :from [:table]
             :where [:= :a :?x]}
            {:params {:x 42} :numbered true})
;;=> ["SELECT * FROM table WHERE a = $1" 42]
(sql/format {:select [:*] :from [:table]
             :where [:= :a [:param :x]]}
            {:params {:x 42} :numbered true})
;;=> ["SELECT * FROM table WHERE a = $1" 42]

Functional Helpers

In addition to the hash map (and sequences) approach of building SQL queries with raw Clojure data structures, a namespace full of helper functions is also available. These functions are generally variadic and threadable:

(require '[honey.sql :as sql]
         '[honey.sql.helpers :refer [select from where]])

(-> (select :t/id [:name :item])
    (from [:table :t])
    (where [:= :id 1])
    (sql/format))
;;=> ["SELECT t.id, name AS item FROM table AS t WHERE id = ?" 1]

There is a helper function for every single clause that HoneySQL supports out of the box. In addition, there are helpers for composite, lateral, over, and upsert that make it easier to construct those parts of the SQL DSL (examples of composite appear in the README, examples of over appear in the Clause Reference)

In addition to being variadic -- which often lets you omit one level of [..] -- the helper functions merge clauses, which can make it easier to build queries programmatically:

(-> (select :t/id)
    (from [:table :t])
    (where [:= :id 1])
    (select [:name :item])
    (sql/format))
;;=> ["SELECT t.id, name AS item FROM table AS t WHERE id = ?" 1]

If you want to replace a clause with a subsequent helper call, you need to explicitly remove the prior value:

(-> (select :t/id)
    (from [:table :t])
    (where [:= :id 1])
    (dissoc :select)
    (select [:name :item])
    (sql/format))
;;=> ["SELECT name AS item FROM table AS t WHERE id = ?" 1]

Helpers always use keywords when constructing clauses so you can rely on using keywords in dissoc.

The following helpers shadow functions in clojure.core so you need to consider this when referring symbols in from the honey.sql.helpers namespace: filter, for, group-by, into, partition-by, set, and update.

DDL Statements

HoneySQL 1.x did not support any DDL statements. It was fairly common for people to use the nilenso/honeysql-postgres library to get DDL support, even if they didn't need the PostgreSQL-specific extensions. That library does not work with HoneySQL 2.x but all of the functionality from it (up to 0.4.112) has been incorporated into HoneySQL now and is described in the PostgreSQL section (because that covers all of the things that the nilenso library supported and much of it was PostgreSQL-specific!).

See also the DDL Clauses section of the Clause Reference for documentation about supported DDL.

Dialects

By default, HoneySQL operates in ANSI SQL mode but it supports a lot of PostgreSQL extensions in that mode. PostgreSQL is mostly a superset of ANSI SQL so it makes sense to support as much as possible of the union of ANSI SQL and PostgreSQL out of the box.

The dialects supported by HoneySQL 2.x are:

• :ansi -- the default, including most PostgreSQL extensions
• :sqlserver -- Microsoft SQL Server
• :mysql -- MySQL (and Percona and MariaDB)
• :oracle -- Oracle

The most visible difference between dialects is how SQL entities should be quoted (if the :quoted true option is provided to format). Most databases use " for quoting (the :ansi and :oracle dialects). The :sqlserver dialect uses [..] and the :mysql dialect uses ... In addition, the :oracle dialect disables AS in aliases.

Note: by default, quoting is off which produces cleaner-looking SQL and assumes you control all the symbols/keywords used as table, column, and function names -- the "SQL entities". If you are building any SQL or DDL where the table, column, or function names could be provided by an external source, you should specify :quoted true to ensure all SQL entities are safely quoted. As of 2.3.928, if you do not specify :quoted as an option, HoneySQL will automatically quote any SQL entities that seem unusual, i.e., that contain any characters that are not alphanumeric or underscore. Purely alphanumeric entities will not be quoted (no entities were quoted by default prior to 2.3.928). You can prevent that auto-quoting by explicitly passing :quoted false into the format call but, from a security point of view, you should think very carefully before you do that: quoting entity names helps protect you from injection attacks! As of 2.4.947, you can change the default setting of :quoted from nil to true (or false) via the set-options! function.

Currently, the only dialect that has substantive differences from the others is :mysql for which the :set clause has a different precedence than ANSI SQL.

You can change the dialect globally using the set-dialect! function, passing in one of the keywords above. You need to call this function before you call format for the first time.

You can change the dialect for a single format call by specifying the :dialect option in that call.

Alphanumeric SQL entities are not quoted by default but if you specify the dialect in a format call, they will be quoted. If you don't specify a dialect in the format call, you can specify :quoted true to have SQL entities quoted. You can also enable quoting globally via the set-dialect! function.

If you want to use a dialect and use the default quoting strategy (automatically quote any SQL entities that seem unusual), specify a :dialect option and set :quoted nil:

(sql/format '{select (id) from (table)} {:quoted true})
;;=> ["SELECT \"id\" FROM \"table\""]
(sql/format '{select (id) from (table)} {:dialect :mysql})
;;=> ["SELECT `id` FROM `table`"]
(sql/set-dialect! :sqlserver)
;;=> nil
(sql/format '{select (id) from (table)} {:quoted true})
;;=> ["SELECT [id] FROM [table]"]
;; you can also choose to enable quoting globally
;; when you set a dialect:
(sql/set-dialect! :mysql :quoted true)
(sql/format '{select (id) from (table)})
;;=> ["SELECT `id` FROM `table`"]
;; and opt out for a specific call:
(sql/format '{select (id) from (table)} {:quoted false})
;;=> ["SELECT id FROM table"]
;; and reset back to the default of :ansi
(sql/set-dialect! :ansi)
;;=> nil
;; which also resets the quoting default (back to nil)
;; so only unusual entity names get quoted:
(sql/format '{select (id) from (table)} {:quoted true})
;;=> ["SELECT \"id\" FROM \"table\""]
;; use default quoting strategy with dialect specific quotes, only unusual entities quoted
(sql/format '{select (id, iffy##field ) from (table)} {:dialect :sqlserver :quoted nil})
;; => ["SELECT id, [iffy##field] FROM table"]

Out of the box, as part of the extended ANSI SQL support, HoneySQL supports quite a few PostgreSQL extensions.

Note: the nilenso/honeysql-postgres library which provided PostgreSQL support for HoneySQL 1.x does not work with HoneySQL 2.x. However, HoneySQL 2.x includes all of the functionality from that library (up to 0.4.112) out of the box!

Reference Documentation

The full list of supported SQL clauses is documented in the Clause Reference. The full list of operators supported (as prefix-form "functions") is documented in the Operator Reference section. The full list of "special syntax" functions is documented in the Special Syntax section. The best documentation for the helper functions is in the honey.sql.helpers namespace. More detail about certain core HoneySQL functionality can be found in the Reference documentation. If you're migrating to HoneySQL 2.x, this overview of differences between 1.x and 2.x should help.