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Dec 31, 2017

SQL builder for Go

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Package sqlbuilder provides a set of flexible and powerful SQL string builders. The only goal of this package is to build SQL string with arguments which can be used in DB#Query or DB#Exec defined in package database/sql.


Use go get to install this package.

go get


Basic usage

We can build a SQL really quick with this package.

sql := sqlbuilder.Select("id", "name").From("demo.user").
    Where("status = 1").Limit(10).


// Output:
// SELECT id, name FROM demo.user WHERE status = 1 LIMIT 10

In the most cases, we need to escape all input from user. In this case, create a builder before starting.

sb := sqlbuilder.NewSelectBuilder()

sb.Select("id", "name", sb.As("COUNT(*)", "c"))
sb.Where(sb.In("status", 1, 2, 5))

sql, args := sb.Build()

// Output:
// SELECT id, name, COUNT(*) AS c FROM user WHERE status IN (?, ?, ?)
// [1 2 5]

Pre-defined SQL builders

Following builders are implemented right now. API document and examples are provided in the godoc document.

There is a method SQL(sql string) implemented by all statement builders like SelectBuilder. We can use this method to insert any arbitrary SQL fragment when building a SQL. It's quite useful to build SQL containing non-standard syntax supported by a OLTP or OLAP system.

// Build a SQL to create a HIVE table.
sql := sqlbuilder.CreateTable("users").
    SQL("PARTITION BY (year)").
        sqlbuilder.Select("columns[0] id", "columns[1] name", "columns[2] year").


// Output:
// CREATE TABLE users PARTITION BY (year) AS SELECT columns[0] id, columns[1] name, columns[2] year FROM `all-users.csv` LIMIT 100

To learn how to use builders, check out examples on GoDoc.

Build SQL for MySQL, PostgreSQL or SQLite

Parameter markers are different in MySQL, PostgreSQL and SQLite. This package provides some methods to set the type of markers (we call it "flavor") in all builders.

By default, all builders uses DefaultFlavor to build SQL. The default value is MySQL.

There is a BuildWithFlavor method in Builder interface. We can use it to build a SQL with provided flavor.

We can wrap any Builder with a default flavor through WithFlavor.

To be more verbose, we can use PostgreSQL.NewSelectBuilder() to create a SelectBuilder with the PostgreSQL flavor. All builders can be created in this way.

Right now, there are only three flavors, MySQL, PostgreSQL and SQLite. Open new issue to me to ask for a new flavor if you find it necessary.

Using Struct as a light weight ORM

Struct stores type information and struct fields of a struct. It's a factory of builders. We can use Struct methods to create initialized SELECT/INSERT/UPDATE/DELETE builders to work with the struct. It can help us to save time and avoid human-error on writing column names.

We can define a struct type and use field tags to let Struct know how to create right builders for us.

type ATable struct {
    Field1     string                                    // If a field doesn't has a tag, use "Field1" as column name in SQL.
    Field2     int    `db:"field2"`                      // Use "db" in field tag to set column name used in SQL.
    Field3     int64  `db:"field3" fieldtag:"foo,bar"`   // Set fieldtag to a field. We can use methods like `Struct#SelectForTag` to use it.
    Field4     int64  `db:"field4" fieldtag:"foo"`       // If we use `s.SelectForTag(table, "foo")`, columnes of SELECT are field3 and field4.
    Ignored    int32  `db:"-"`                           // If we set field name as "-", Struct will ignore it.
    unexported int                                       // Unexported field is not visible to Struct.
    Quoted     string `db:"quoted" fieldopt:"withquote"` // Add quote to the field using back quote or double quote. See `Flavor#Quote`.
    Empty      uint   `db:"empty" fieldopt:"omitempty"`  // Omit the field in UPDATE if it is a nil or zero value.

    // The `omitempty` can be written as a function.
    // In this case, omit empty field `Tagged` when UPDATE for tag `tag1` and `tag3` but not `tag2`.
    Tagged     string `db:"tagged" fieldopt:"omitempty(tag1,tag3)" fieldtag:"tag1,tag2,tag3"`

Read examples for Struct to learn details of how to use it.

What's more, we can use Struct as a kind of zero-config ORM. While most ORM implementations requires several prerequisite configs to work with database connections, Struct doesn't require any config and work well with any SQL driver which works with database/sql. Struct doesn't call any database/sql API; It just creates right SQL with arguments for DB#Query/DB#Exec or a slice of address of struct fields for Rows#Scan/Row#Scan.

Here is a sample to use Struct as ORM. It should be quite straight forward for developers who are familiar with database/sql APIs.

type User struct {
    ID     int64  `db:"id"`
    Name   string `db:"name"`
    Status int    `db:"status"`

// A global variable to create SQL builders.
// All methods of userStruct are thread-safe.
var userStruct = NewStruct(new(User))

func ExampleStruct() {
    // Prepare SELECT query.
    //     SELECT id, name, status FROM user WHERE id = 1234
    sb := userStruct.SelectFrom("user")
    sb.Where(sb.Equal("id", 1234))

    // Execute the query.
    sql, args := sb.Build()
    rows, _ := db.Query(sql, args...)
    defer rows.Close()

    // Scan row data and set value to user.
    // Suppose we get following data.
    //     |  id  |  name  | status |
    //     |------|--------|--------|
    //     | 1234 | huandu | 1      |
    var user User

    fmt.Printf("%#v", user)

    // Output:
    // SELECT,, user.status FROM user WHERE id = ?
    // [1234]
    // sqlbuilder.User{ID:1234, Name:"huandu", Status:1}

In many production environments, table column names are usually snake_case words, e.g. user_id, while we have to use CamelCase in struct types to make struct fields public and golint happy. It's a bit redundant to use the db tag in every struct field. If there is a certain rule to map field names to table column names, We can use field mapper function to make code simpler.

The DefaultFieldMapper is a global field mapper function to convert field name to new style. By default, it sets to nil and does nothing. If we know that most table column names are snake_case words, we can set DefaultFieldMapper to sqlbuilder.SnakeCaseMapper. If we have some special cases, we can set custom mapper to a Struct by calling WithFieldMapper.

Following are special notes regarding to field mapper.

  • Field tag has precedence over field mapper function - thus, mapper is ignored if the db tag is set;
  • Field mapper is called only once on a Struct when the Struct is used to create builder for the first time.

See field mapper function sample as a demo.

Nested SQL

It's quite straight forward to create a nested SQL: use a builder as an argument to nest it.

Here is a sample.

sb := sqlbuilder.NewSelectBuilder()
fromSb := sqlbuilder.NewSelectBuilder()
statusSb := sqlbuilder.NewSelectBuilder()

sb.From(sb.BuilderAs(fromSb, "user")))
sb.Where(sb.In("status", statusSb))

fromSb.Select("id").From("user").Where(fromSb.GreaterThan("level", 4))
statusSb.Select("status").From("config").Where(statusSb.Equal("state", 1))

sql, args := sb.Build()

// Output:
// SELECT id FROM (SELECT id FROM user WHERE level > ?) AS user WHERE status IN (SELECT status FROM config WHERE state = ?)
// [4 1]

Use sql.Named in a builder

The function sql.Named defined in database/sql can create a named argument in SQL. It's necessary if we want to reuse an argument several times in one SQL. It's still quite simple to use named arguments in a builder: use it as an argument.

Here is a sample.

now := time.Now().Unix()
start := sql.Named("start", now-86400)
end := sql.Named("end", now+86400)
sb := sqlbuilder.NewSelectBuilder()

    sb.Between("created_at", start, end),
    sb.GE("modified_at", start),

sql, args := sb.Build()

// Output:
// SELECT name FROM user WHERE created_at BETWEEN @start AND @end AND modified_at >= @start
// [{{} start 1514458225} {{} end 1514544625}]

Argument modifiers

There are several modifiers for arguments.

  • List(arg) represents a list of arguments. If arg is a slice or array, e.g. a slice with 3 ints, it will be compiled to ?, ?, ? and flattened in the final arguments as 3 ints. It's a tool for convenience. We can use it in the IN expression or VALUES of INSERT INTO.
  • Named(name, arg) represents a named argument. It only works with Build or BuildNamed to define a named placeholder using syntax ${name}.
  • Raw(expr) marks an expr as a plain string in SQL rather than an argument. When we build a builder, the value of raw expressions are copied in SQL string directly without leaving any ? in SQL.

Freestyle builder

A builder is only a way to record arguments. If we want to build a long SQL with lots of special syntax (e.g. special comments for a database proxy), simply use Buildf to format a SQL string using a fmt.Sprintf-like syntax.

sb := sqlbuilder.NewSelectBuilder()

explain := sqlbuilder.Buildf("EXPLAIN %v LEFT JOIN SELECT * FROM banned WHERE state IN (%v, %v)", sb, 1, 2)
sql, args := explain.Build()

// Output:
// [1 2]

Using special syntax to build SQL

Package sqlbuilder defines special syntax to represent an uncompiled SQL internally. If we want to take advantage of the syntax to build customized tools, we can use Build to compile it with arguments.

The format string uses special syntax to represent arguments.

  • $? refers successive arguments passed in the call. It works similar as %v in fmt.Sprintf.
  • $0 $1 ... $n refers nth-argument passed in the call. Next $? will use arguments n+1.
  • ${name} refers a named argument created by Named with name.
  • $$ is a "$" string.
sb := sqlbuilder.NewSelectBuilder()
sb.Select("id").From("user").Where(sb.In("status", 1, 2))

b := sqlbuilder.Build("EXPLAIN $? LEFT JOIN SELECT * FROM $? WHERE created_at > $? AND state IN (${states}) AND modified_at BETWEEN $2 AND $?",
    sb, sqlbuilder.Raw("banned"), 1514458225, 1514544625, sqlbuilder.Named("states", sqlbuilder.List([]int{3, 4, 5})))
sql, args := b.Build()


// Output:
// EXPLAIN SELECT id FROM user WHERE status IN (?, ?) LEFT JOIN SELECT * FROM banned WHERE created_at > ? AND state IN (?, ?, ?) AND modified_at BETWEEN ? AND ?
// [1 2 1514458225 3 4 5 1514458225 1514544625]

If we just want to use ${name} syntax to refer named arguments, use BuildNamed instead. It disables all special syntax but ${name} and $$.

Interpolate args in the sql

Some SQL drivers doesn't actually implement StmtExecContext#ExecContext. They will fail when len(args) > 0. The only solution is to interpolate args in the sql, and execute the interpolated query with the driver.

Security warning: I try my best to escape special characters in interpolate methods, but it's still less secure than Stmt implemented by SQL servers.

This feature is inspired by interpolation feature in package

Here is a sample for MySQL.

sb := MySQL.NewSelectBuilder()
    sb.NE("id", 1234),
    sb.E("name", "Charmy Liu"),
    sb.Like("desc", "%mother's day%"),
sql, args := sb.Build()
query, err := MySQL.Interpolate(sql, args)


// Output:
// SELECT name FROM user WHERE id <> 1234 AND name = 'Charmy Liu' AND desc LIKE '%mother\'s day%'
// <nil>

Here is a sample for PostgreSQL. Note that the dollar quote is supported.

// Only the last `$1` is interpolated.
// Others are not interpolated as they are inside dollar quote (the `$$`).
query, err := PostgreSQL.Interpolate(`
CREATE FUNCTION dup(in int, out f1 int, out f2 text) AS $$
    SELECT $1, CAST($1 AS text) || ' is text'

SELECT * FROM dup($1);`, []interface{}{42})


// Output:
// CREATE FUNCTION dup(in int, out f1 int, out f2 text) AS $$
//     SELECT $1, CAST($1 AS text) || ' is text'
// $$
// SELECT * FROM dup(42);
// <nil>


What's the difference between this package and squirrel

Package squirrel is another SQL builder package with outstanding design and high code quality. Comparing with squirrel, go-sqlbuilder is much more extensible with more built-in features.

Here are details.

  • API design: The core of go-sqlbuilder is Builder and Args. Nearly all features are built on top of them. If we want to extend this package, e.g. support EXPLAIN, we can use Build("EXPLAIN $?", builder) to add EXPLAIN in front of any SQL.
  • ORM: Package squirrel doesn't provide ORM directly. There is another package structable, which is based on squirrel, designed for ORM.
  • No design pitfalls: There is no design pitfalls like squirrel.Eq{"mynumber": []uint8{1,2,3}}. I'm proud of it. :)


This package is licensed under MIT license. See LICENSE for details.