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Expressions

    +

    SQL++ is a highly composable expression language. Each SQL++ expression returns zero or more data model instances. There are three major kinds of expressions in SQL++. At the topmost level, a SQL++ expression can be an OperatorExpression (similar to a mathematical expression), an ConditionalExpression (to choose between alternative values), or a QuantifiedExpression (which yields a boolean value). Each will be detailed as we explore the full SQL++ grammar.

    Expression ::= OperatorExpression | CaseExpression | QuantifiedExpression

    Note that in the following text, words enclosed in angle brackets denote keywords that are not case-sensitive.

    Operator Expressions

    Operators perform a specific operation on the input values or expressions. The syntax of an operator expression is as follows:

    OperatorExpression ::= PathExpression
                       | Operator OperatorExpression
                       | OperatorExpression Operator (OperatorExpression)?
                       | OperatorExpression <BETWEEN> OperatorExpression <AND> OperatorExpression

    SQL++ provides a full set of operators that you can use within its statements. Here are the categories of operators:

    The following table summarizes the precedence order (from higher to lower) of the major unary and binary operators:

    Operator Operation

    EXISTS, NOT EXISTS

    Collection emptiness testing

    ^

    Exponentiation

    *, /, %

    Multiplication, division, modulo

    +, -

    Addition, subtraction

    ||

    String concatenation

    IS NULL, IS NOT NULL, IS MISSING, IS NOT MISSING,
    IS UNKNOWN, IS NOT UNKNOWN, IS VALUED, IS NOT VALUED

    Unknown value comparison

    BETWEEN, NOT BETWEEN

    Range comparison (inclusive on both sides)

    =, !=, <>, <, >, <=, >=, LIKE, NOT LIKE, IN, NOT IN

    Comparison

    NOT

    Logical negation

    AND

    Conjunction

    OR

    Disjunction

    In general, if any operand evaluates to a MISSING value, the enclosing operator will return MISSING; if none of operands evaluates to a MISSING value but there is an operand evaluates to a NULL value, the enclosing operator will return NULL. However, there are a few exceptions listed in comparison operators and logical operators.

    Arithmetic Operators

    Arithmetic operators are used to exponentiate, add, subtract, multiply, and divide numeric values, or concatenate string values.

    Operator Purpose Example

    +, -

    As unary operators, they denote a
    positive or negative expression

    SELECT VALUE -1;

    +, -

    As binary operators, they add or subtract

    SELECT VALUE 1 + 2;

    *, /, %

    Multiply, divide, modulo

    SELECT VALUE 4 / 2.0;

    ^

    Exponentiation

    SELECT VALUE 2^3;

    ||

    String concatenation

    SELECT VALUE "ab"||"c"||"d";

    Collection Operators

    Collection operators are used for membership tests (IN, NOT IN) or empty collection tests (EXISTS, NOT EXISTS).

    Operator Purpose Example

    IN

    Membership test

    SELECT * FROM ChirpMessages cm
    WHERE cm.user.lang IN ["en", "de"];

    NOT IN

    Non-membership test

    SELECT * FROM ChirpMessages cm
    WHERE cm.user.lang NOT IN ["en"];

    EXISTS

    Check whether a collection is not empty

    SELECT * FROM ChirpMessages cm
    WHERE EXISTS cm.referredTopics;

    NOT EXISTS

    Check whether a collection is empty

    SELECT * FROM ChirpMessages cm
    WHERE NOT EXISTS cm.referredTopics;

    Comparison Operators

    Comparison operators are used to compare values. The comparison operators fall into one of two sub-categories: missing value comparisons and regular value comparisons. SQL++ (and JSON) has two ways of representing missing information in a object - the presence of the field with a NULL for its value (as in SQL), and the absence of the field (which JSON permits). For example, the first of the following objects represents Jack, whose friend is Jill. In the other examples, Jake is friendless a la SQL, with a friend field that is NULL, while Joe is friendless in a more natural (for JSON) way, i.e., by not having a friend field.

    Examples

    {"name": "Jack", "friend": "Jill"}

    {"name": "Jake", "friend": NULL}

    {"name": "Joe"}

    The following table enumerates all of SQL++'s comparison operators.

    Operator Purpose Example

    IS NULL

    Test if a value is NULL

    SELECT * FROM ChirpMessages cm
    WHERE cm.user.name IS NULL;

    IS NOT NULL

    Test if a value is not NULL

    SELECT * FROM ChirpMessages cm
    WHERE cm.user.name IS NOT NULL;

    IS MISSING

    Test if a value is MISSING

    SELECT * FROM ChirpMessages cm
    WHERE cm.user.name IS MISSING;

    IS NOT MISSING

    Test if a value is not MISSING

    SELECT * FROM ChirpMessages cm
    WHERE cm.user.name IS NOT MISSING;

    IS UNKNOWN

    Test if a value is NULL or MISSING

    SELECT * FROM ChirpMessages cm
    WHERE cm.user.name IS UNKNOWN;

    IS NOT UNKNOWN

    Test if a value is neither NULL nor MISSING

    SELECT * FROM ChirpMessages cm
    WHERE cm.user.name IS NOT UNKNOWN;

    IS VALUED

    Test if a value is neither NULL nor MISSING

    SELECT * FROM ChirpMessages cm
    WHERE cm.user.name IS VALUED;

    IS NOT VALUED

    Test if a value is NULL or MISSING

    SELECT * FROM ChirpMessages cm
    WHERE cm.user.name IS NOT VALUED;

    BETWEEN

    Test if a value is between a start value and
    a end value. The comparison is inclusive
    to both start and end values.

    SELECT * FROM ChirpMessages cm
    WHERE cm.chirpId BETWEEN 10 AND 20;

    =

    Equality test

    SELECT * FROM ChirpMessages cm
    WHERE cm.chirpId=10;

    !=

    Inequality test

    SELECT * FROM ChirpMessages cm
    WHERE cm.chirpId!=10;

    <>

    Inequality test

    SELECT * FROM ChirpMessages cm
    WHERE cm.chirpId<>10;

    <

    Less than

    SELECT * FROM ChirpMessages cm
    WHERE cm.chirpId<10;

    >

    Greater than

    SELECT * FROM ChirpMessages cm
    WHERE cm.chirpId>10;

    <=

    Less than or equal to

    SELECT * FROM ChirpMessages cm
    WHERE cm.chirpId<=10;

    >=

    Greater than or equal to

    SELECT * FROM ChirpMessages cm
    WHERE cm.chirpId>=10;

    LIKE

    Test if the left side matches a
    pattern defined on the right
    side; in the pattern, "%" matches
    any string while "_" matches
    any character.

    SELECT * FROM ChirpMessages cm
    WHERE cm.user.name LIKE "%Giesen%";

    NOT LIKE

    Test if the left side does not
    match a pattern defined on the right
    side; in the pattern, "%" matches
    any string while "_" matches
    any character.

    SELECT * FROM ChirpMessages cm
    WHERE cm.user.name NOT LIKE "%Giesen%";

    The following table summarizes how the missing value comparison operators work.

    Operator Non-NULL/Non-MISSING value NULL MISSING

    IS NULL

    FALSE

    TRUE

    MISSING

    IS NOT NULL

    TRUE

    FALSE

    MISSING

    IS MISSING

    FALSE

    FALSE

    TRUE

    IS NOT MISSING

    TRUE

    TRUE

    FALSE

    IS UNKNOWN

    FALSE

    TRUE

    TRUE

    IS NOT UNKNOWN

    TRUE

    FALSE

    FALSE

    IS VALUED

    TRUE

    FALSE

    FALSE

    IS NOT VALUED

    FALSE

    TRUE

    TRUE

    Logical Operators

    Logical operators perform logical NOT, AND, and OR operations over Boolean values (TRUE and FALSE) plus NULL and MISSING.

    Operator Purpose Example

    NOT

    Returns true if the following condition is false, otherwise returns false

    SELECT VALUE NOT TRUE;

    AND

    Returns true if both branches are true, otherwise returns false

    SELECT VALUE TRUE AND FALSE;

    OR

    Returns true if one branch is true, otherwise returns false

    SELECT VALUE FALSE OR FALSE;

    The following table is the truth table for AND and OR.

    A B A AND B A OR B

    TRUE

    TRUE

    TRUE

    TRUE

    TRUE

    FALSE

    FALSE

    TRUE

    TRUE

    NULL

    NULL

    TRUE

    TRUE

    MISSING

    MISSING

    TRUE

    FALSE

    FALSE

    FALSE

    FALSE

    FALSE

    NULL

    FALSE

    NULL

    FALSE

    MISSING

    FALSE

    MISSING

    NULL

    NULL

    NULL

    NULL

    NULL

    MISSING

    MISSING

    NULL

    MISSING

    MISSING

    MISSING

    MISSING

    The following table demonstrates the results of NOT on all possible inputs.

    A NOT A

    TRUE

    FALSE

    FALSE

    TRUE

    NULL

    NULL

    MISSING

    MISSING

    Case Expressions

    CaseExpression ::= SimpleCaseExpression | SearchedCaseExpression
SimpleCaseExpression ::= <CASE> Expression ( <WHEN> Expression <THEN> Expression )+ ( <ELSE> Expression )? <END>
SearchedCaseExpression ::= <CASE> ( <WHEN> Expression <THEN> Expression )+ ( <ELSE> Expression )? <END>

    In a simple CASE expression, the query evaluator searches for the first WHEN …​ THEN pair in which the WHEN expression is equal to the expression following CASE and returns the expression following THEN. If none of the WHEN …​ THEN pairs meet this condition, and an ELSE branch exists, it returns the ELSE expression. Otherwise, NULL is returned.

    In a searched CASE expression, the query evaluator searches from left to right until it finds a WHEN expression that is evaluated to TRUE, and then returns its corresponding THEN expression. If no condition is found to be TRUE, and an ELSE branch exists, it returns the ELSE expression. Otherwise, it returns NULL.

    The following example illustrates the form of a case expression.

    Example
    CASE (2 < 3) WHEN true THEN "yes" ELSE "no" END

    Quantified Expressions

    QuantifiedExpression ::= ( (<ANY>|<SOME>) | <EVERY> ) Variable <IN> Expression ( "," Variable "in" Expression )*
                         <SATISFIES> Expression (<END>)?

    Quantified expressions are used for expressing existential or universal predicates involving the elements of a collection.

    The following pair of examples illustrate the use of a quantified expression to test that every (or some) element in the set [1, 2, 3] of integers is less than three. The first example yields FALSE and second example yields TRUE.

    It is useful to note that if the set were instead the empty set, the first expression would yield TRUE ("every" value in an empty set satisfies the condition) while the second expression would yield FALSE (since there isn’t "some" value, as there are no values in the set, that satisfies the condition).

    A quantified expression will return a NULL (or MISSING) if the first expression in it evaluates to NULL (or MISSING). A type error will be raised if the first expression in a quantified expression does not return a collection.

    Examples
    EVERY x IN [ 1, 2, 3 ] SATISFIES x < 3
SOME x IN [ 1, 2, 3 ] SATISFIES x < 3

    Path Expressions

    PathExpression  ::= PrimaryExpression ( Field | Index )*
Field           ::= "." Identifier
Index           ::= "[" ( Expression | "?" ) "]"

    Components of complex types in the data model are accessed via path expressions. Path access can be applied to the result of a SQL++ expression that yields an instance of a complex type, for example, a object or array instance. For objects, path access is based on field names. For arrays, path access is based on (zero-based) array-style indexing. SQL++ also supports an "I’m feeling lucky" style index accessor, [?], for selecting an arbitrary element from an array. Attempts to access non-existent fields or out-of-bound array elements produce the special value MISSING. Type errors will be raised for inappropriate use of a path expression, such as applying a field accessor to a numeric value.

    The following examples illustrate field access for a object, index-based element access for an array, and also a composition thereof.

    Examples
    ({"name": "MyABCs", "array": [ "a", "b", "c"]}).array

(["a", "b", "c"])[2]

({"name": "MyABCs", "array": [ "a", "b", "c"]}).array[2]

    Primary Expressions

    PrimaryExpr ::= Literal
              | VariableReference
              | ParenthesizedExpression
              | FunctionCallExpression
              | Constructor

    The most basic building block for any SQL++ expression is PrimaryExpression. This can be a simple literal (constant) value, a reference to a query variable that is in scope, a parenthesized expression, a function call, or a newly constructed instance of the data model (such as a newly constructed object, array, or multiset of data model instances).

    Literals

    Literal        ::= StringLiteral
                   | IntegerLiteral
                   | FloatLiteral
                   | DoubleLiteral
                   | <NULL>
                   | <MISSING>
                   | <TRUE>
                   | <FALSE>
StringLiteral  ::= "\"" (
                             <EscapeQuot>
                           | <EscapeBslash>
                           | <EscapeSlash>
                           | <EscapeBspace>
                           | <EscapeFormf>
                           | <EscapeNl>
                           | <EscapeCr>
                           | <EscapeTab>
                           | ~["\"","\\"])*
                    "\""
                    | "\'"(
                             <EscapeApos>
                           | <EscapeBslash>
                           | <EscapeSlash>
                           | <EscapeBspace>
                           | <EscapeFormf>
                           | <EscapeNl>
                           | <EscapeCr>
                           | <EscapeTab>
                           | ~["\'","\\"])*
                      "\'"
<ESCAPE_Apos>  ::= "\\\'"
<ESCAPE_Quot>  ::= "\\\""
<EscapeBslash> ::= "\\\\"
<EscapeSlash>  ::= "\\/"
<EscapeBspace> ::= "\\b"
<EscapeFormf>  ::= "\\f"
<EscapeNl>     ::= "\\n"
<EscapeCr>     ::= "\\r"
<EscapeTab>    ::= "\\t"

IntegerLiteral ::= <DIGITS>
<DIGITS>       ::= ["0" - "9"]+
FloatLiteral   ::= <DIGITS> ( "f" | "F" )
                 | <DIGITS> ( "." <DIGITS> ( "f" | "F" ) )?
                 | "." <DIGITS> ( "f" | "F" )
DoubleLiteral  ::= <DIGITS> "." <DIGITS>
                   | "." <DIGITS>

    Literals (constants) in SQL++ can be strings, integers, floating point values, double values, boolean constants, or special constant values like NULL and MISSING. The NULL value is like a NULL in SQL; it is used to represent an unknown field value. The specialy value MISSING is only meaningful in the context of SQL++ field accesses; it occurs when the accessed field simply does not exist at all in a object being accessed.

    The following are some simple examples of SQL++ literals.

    Examples
    'a string'
"test string"
42

    Different from standard SQL, double quotes play the same role as single quotes and may be used for string literals in SQL++.

    Variable References

    VariableReference     ::= <IDENTIFIER>|<DelimitedIdentifier>
<IDENTIFIER>          ::= (<LETTER> | "_") (<LETTER> | <DIGIT> | "_" | "$")*
<LETTER>              ::= ["A" - "Z", "a" - "z"]
DelimitedIdentifier   ::= "`" (<EscapeQuot>
                                | <EscapeBslash>
                                | <EscapeSlash>
                                | <EscapeBspace>
                                | <EscapeFormf>
                                | <EscapeNl>
                                | <EscapeCr>
                                | <EscapeTab>
                                | ~["`","\\"])*
                          "`"

    A variable in SQL++ can be bound to any legal data model value. A variable reference refers to the value to which an in-scope variable is bound. (E.g., a variable binding may originate from one of the FROM, WITH or LET clauses of a SELECT statement or from an input parameter in the context of a function body.) Backticks, for example, id, are used for delimited identifiers. Delimiting is needed when a variable’s desired name clashes with a SQL++ keyword or includes characters not allowed in regular identifiers. More information on exactly how variable references are resolved can be found in the appendix section on Variable Resolution.

    Examples
    tweet
id
`SELECT`
`my-function`

    Parenthesized Expressions

    ParenthesizedExpression ::= "(" Expression ")" | Subquery

    An expression can be parenthesized to control the precedence order or otherwise clarify a query. In SQL++, for composability, a subquery is also an parenthesized expression.

    The following expression evaluates to the value 2.

    Example
    ( 1 + 1 )

    Function Call Expressions

    FunctionCallExpression ::= FunctionName "(" ( Expression ( "," Expression )* )? ")"

    Functions are included in SQL++, like most languages, as a way to package useful functionality or to componentize complicated or reusable SQL++ computations. A function call is a legal SQL++ query expression that represents the value resulting from the evaluation of its body expression with the given parameter bindings; the parameter value bindings can themselves be any SQL++ expressions.

    The following example is a (built-in) function call expression whose value is 8.

    Example
    length('a string')

    Constructors

    Constructor              ::= ArrayConstructor | MultisetConstructor | ObjectConstructor
ArrayConstructor         ::= "[" ( Expression ( "," Expression )* )? "]"
MultisetConstructor      ::= "{{" ( Expression ( "," Expression )* )? "}}"
ObjectConstructor        ::= "{" ( FieldBinding ( "," FieldBinding )* )? "}"
FieldBinding             ::= Expression ":" Expression

    A major feature of SQL++ is its ability to construct new data model instances. This is accomplished using its constructors for each of the model’s complex object structures, namely arrays, multisets, and objects. Arrays are like JSON arrays, while multisets have bag semantics. Objects are built from fields that are field-name/field-value pairs, again like JSON.

    The following examples illustrate how to construct a new array with 4 items and a new object with 2 fields respectively. Array elements can be homogeneous (as in the first example), which is the common case, or they may be heterogeneous (as in the second example). The data values and field name values used to construct arrays, multisets, and objects in constructors are all simply SQL++ expressions. Thus, the collection elements, field names, and field values used in constructors can be simple literals or they can come from query variable references or even arbitrarily complex SQL++ expressions (subqueries). Type errors will be raised if the field names in an object are not strings, and duplicate field errors will be raised if they are not distinct.

    Examples
    [ 'a', 'b', 'c', 'c' ]

[ 42, "forty-two!", { "rank" : "Captain", "name": "America" }, 3.14159 ]

{
  'project name': 'Hyracks',
  'project members': [ 'vinayakb', 'dtabass', 'chenli', 'tsotras', 'tillw' ]
}