Select ClickHouse

• API
• Example
• Columnar
• Count rows
• Subqueries

API

For the full list of supported methods, see SelectQuery.

db.NewSelect().
	With("cte_name", subquery).
    WithAlias("name", "? + ?", args...).

	Model(&strct).
	Model(&slice).

	Column("col1", "col2"). // quotes column names
	ColumnExpr("col1, col2"). // arbitrary unsafe expression
	ColumnExpr("count(*)").
	ColumnExpr("count(?)", ch.Ident("id")).
	ColumnExpr("(?) AS alias", subquery).
	ExcludeColumn("col1"). // all columns except col1
	ExcludeColumn("*"). // exclude all columns

	Table("table1", "table2"). // quotes table names
	TableExpr("table1 AS t1"). // arbitrary unsafe expression
	TableExpr("(?) AS alias", subquery).
	ModelTableExpr("table1 AS t1"). // overrides model table name
    Sample("1000000"). // sample 1 million rows

	Join("JOIN table2 AS t2 ON t2.id = t1.id").
	Join("LEFT JOIN table2 AS t2").JoinOn("t2.id = t1.id").

	Where("id = ?", 123).
	Where("name LIKE ?", "my%").
	Where("? = 123", ch.Ident("id")).
	Where("id IN (?)", ch.In([]int64{1, 2, 3})).
	Where("id IN (?)", subquery).
	Where("FALSE").WhereOr("TRUE").
	WhereGroup(" AND ", func(q *ch.SelectQuery) *ch.SelectQuery {
		return q.WhereOr("id = 1").
			WhereOr("id = 2")
	}).

	Group("col1", "col2"). // quotes column names
	GroupExpr("lower(col1)"). // arbitrary unsafe expression

	Order("col1 ASC", "col2 DESC"). // quotes column names
	OrderExpr("col1 ASC NULLS FIRST"). // arbitrary unsafe expression

    Having("column_name > ?", 123).

	Limit(100).
	Offset(100).

    Setting("prefer_column_name_to_alias = 1").

	Scan(ctx)

Example

To select data from ClickHouse, define a model and use SelectQuery:

type Span struct {
	ID	 uint64
	Name string
}

span := new(Span)
err := db.NewSelect().Model(span).Where("id = ?", 123).Scan(ctx)

To select multiple rows:

var spans []Span
err := db.NewSelect().Model(&spans).Limit(1000).Scan(ctx)

You can also select into a map:

var m map[string]interface{}
err := db.NewSelect().Model((*Span)(nil)).Where("id = ?", 123).Scan(ctx, &m)

Columnar

If you want to select whole columns from ClickHouse, you can use the ,columnar option:

type Model struct {
	ch.CHModel `ch:",columnar"`

    Col1 []string
    Col2 []uint64
    Col3 []time.Time
}

model := new(Model)
err := db.NewSelect().Model(model).Limit(1000).Scan(ctx)

Count rows

go-clickhouse provides Count helper to generate count() queries:

count, err := db.NewSelect().Model((*User)(nil)).Count(ctx)

Because selecting and counting rows is a common operation, the client also provides ScanAndCount:

var users []User
count, err := db.NewSelect().Model(&users).Limit(20).ScanAndCount(ctx)
if err != nil {
	panic(err)
}
fmt.Println(users, count)

Subqueries

You can use go-clickhouse queries as a subquery:

subq := db.NewSelect().Model((*Book)(nil)).Where("author_id = ?", 1)

err := db.NewSelect().Model().TableExpr("(?) AS book", subq).Scan(ctx, &books)

SELECT * FROM (
  SELECT "book"."id", "book"."title", "book"."text"
  FROM "books" AS "book"
  WHERE (author_id = 1)
) AS book