package petrol

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Module Petrol.ExprSource

Provides an SQL E-DSL for writing well-typed SQL expressions.

Sourcetype 'a t

'a t represents an SQL expression that produces a value corresponding to the type 'a.

Sourcetype 'a expr_list =
  1. | [] : unit expr_list
  2. | :: : ('a t * 'b expr_list) -> ('a * 'b) expr_list

Represents a heterogeneous sequence of SQL expressions.

Note Provided you have opened the Expr module, you can use List syntax to construct such lists:

  Petrol.Expr.[i 1; bl false]
  (* - : (int * (bool * ())) Petrol.Expr.expr_list *)
Sourcetype wrapped_assign

An opaque wrapper that represents an assignment of a value to a particular field in a table.

Sourceval pp : Format.formatter -> 'a t -> unit

pp fmt expr pretty prints an SQL expression as a string that can be parsed by an SQL engine.

Constants

The following functions define constant value expressions.

Note For each type, there are two flavours of constant expression: variable and static.

The key difference between the two is in terms of how they are represented in the final SQL query - in particular, variable constant expressions are encoded as holes (?) in the query, to which a constant value is supplied, whereas static constant expressions are encoded directly in the query string.

As Petrol functions cache the construction of SQL queries by their final string representation, you should prefer the dynamic form if you expect the constant value to change frequently - for example, if it is a constant value that you are receiving from elsewhere. Use the static form if you know that the value doesn't change and will always be the same.

Sourceval i : int -> int t

i v returns an expression that evaluates to the integer value v.

Sourceval f : float -> float t

f v returns an expression that evaluates to the real value v.

Sourceval s : string -> string t

s v returns an expression that evaluates to the string value v.

Sourceval b : string -> string t

b v returns an expression that evaluates to the bytes value v.

Sourceval bl : bool -> bool t

bl v returns an expression that evaluates to the bool value v.

Sourceval i_stat : int -> int t

i_stat v returns a static expression that evaluates to the integer value v.

Sourceval f_stat : float -> float t

f_stat v returns a static expression that evaluates to the real value v.

Sourceval s_stat : string -> string t

s_stat v returns a static expression that evaluates to the string value v.

Sourceval b_stat : string -> string t

b_stat v returns a static expression that evaluates to the bytes value v.

Sourceval true_ : bool t

true_ represents the SQL constant TRUE.

Sourceval false_ : bool t

false_ represents the SQL constant FALSE.

Book-keeping: Types, Naming, Nulls

Sourceval as_ : 'a t -> name:string -> 'a t * 'a t

as_ exp ~name returns a tuple (exp',exp'_ref) where exp' is the SQL expression exp AS name that names exp as name, and exp'_ref is simply name.

Sourceval nullable : 'a t -> 'a option t

nullable e encodes the fact that the expression e may return NULL.

Sourceval is_not_null : 'a t -> bool t

is_not_null e constructs an SQL expression that is TRUE iff the expression e is not NULL and FALSE otherwise.

Sourceval coerce : 'a t -> 'b Type.t -> 'b t

coerce expr ty coerces expression expr to the type ty. This coercion is not checked, so make sure you know what you're doing or it could fail at runtime.

Sourceval (:=) : 'a t -> 'a t -> wrapped_assign

v := expr returns an SQL expression that can be used with an update or insert clause to change the values in the database.

Operators

Sourceval (+) : int t -> int t -> int t
Sourceval (-) : int t -> int t -> int t
Sourceval (=) : 'a t -> 'a t -> bool t
Sourceval (<>) : 'a t -> 'a t -> bool t
Sourceval (<=) : 'a t -> 'a t -> bool t
Sourceval (<) : 'a t -> 'a t -> bool t
Sourceval (>) : 'a t -> 'a t -> bool t
Sourceval (>=) : 'a t -> 'a t -> bool t
Sourceval (&&) : bool t -> bool t -> bool t
Sourceval (||) : bool t -> bool t -> bool t

Functions

Sourceval count : ?distinct:bool -> 'a expr_list -> int t
Sourceval count_star : int t
Sourceval max : ?distinct:bool -> int t -> int t
Sourceval min : ?distinct:bool -> int t -> int t
Sourceval sum : ?distinct:bool -> int t -> int t
Sourceval total : ?distinct:bool -> int t -> int t
Sourceval group_concat : ?distinct:bool -> ?sep_by:string t -> string t -> string t
Sourceval abs : int t -> int t
Sourceval changes : int t
Sourceval glob : pat:string t -> string t -> bool t
Sourceval coalesce : 'a t list -> 'a t
Sourceval like : string t -> pat:string t -> bool t
Sourceval max_of : int t list -> int t
Sourceval min_of : int t list -> int t
Sourceval random : int t
Sourceval lower : string t -> string t
Sourceval upper : string t -> string t