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:

    seancorfield/honeysql {:mvn/version "2.0.0-alpha1"}

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

    [seancorfield/honeysql "2.0.0-alpha1"]

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.

Basic Concepts

SQL statements are represented as hash maps, with keys that represent clauses in SQL. SQL expressions are generally represented as vectors, 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:

(ns my.example
  (:require [honey.sql :as sql]))

(sql/format {:select [:*], :from [:table], :where [:= :id 1]})
;; produces:
;;=> ["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 vector 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 most 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]})
;; produces:
;;=> ["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]})
;; or you can use (..) instead of [..] when quoted:
(sql/format '{select (t.id (name item)), from ((table t)), where (= id 1)})
;; also produces:
;;=> ["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:

(sql/format {:select [:t/id [:name :item]], :from [[:table :t]], :where [:= :id 1]})
;; and
(sql/format '{select [t/id [name item]], from [[table t]], where [= id 1]})
;; both produce:
;;=> ["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 vectors 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).

Operators can be strictly binary or variadic (most are strictly binary). 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)

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. 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

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]

Functional Helpers

In addition to the hash map (and vectors) 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:

(ns my.example
  (: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))
;; produces:
;;=> ["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 and over that make it easier to construct those parts of the SQL DSL (examples of the former appear in the README, examples of the latter 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))
;; produces:
;;=> ["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))
;; produces:
;;=> ["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: for, group-by, partition-by, set, and update.

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 v2 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 ...

Currently, the only dialect that has substantive differences from the others is :mysql which has a :lock clause (that is very similar to the ANSI :for clause) and 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.

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.

(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]"]

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

Format Options

In addition to the :quoted and :dialect options described above, format also accepts :inline and :params.

The :params option was mentioned above and is used to specify the values of named parameters in the DSL.

The :inline option suppresses the generation of parameters in the SQL string and instead tries to inline all the values directly into the SQL string. The behavior is as if each value in the DSL was wrapped in [:inline..]:

• nil becomes the SQL value NULL,
• Clojure strings become inline SQL strings with single quotes (so "foo" becomes 'foo'),
• keywords and symbols become SQL keywords (uppercase, with - replaced by a space),
• everything else is just turned into a string (by calling str) and added to the SQL string.

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. If you're migrating to HoneySQL 2.0, this overview of differences between 1.0 and 2.0 should help.