add table of operator precedence to HQL guide
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Gavin
Christian Beikov
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@ -191,7 +191,7 @@ But in SQL, and therefore also in HQL and JPQL, such an expression evaluates to
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It's almost always the case that an operation applied to a null value yields another null value.
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This applies to function application, to operators like `*` and `||`, to comparison operators like `<` and `=`, and even to logical operations like `and` and `not`.
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The exceptions to this rule are the functions `coalesce()` and `ifnull()` which are specifically designed for <<functions-null,dealing with null values>>.
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The exceptions to this rule are the `is null` operator and the functions `coalesce()` and `ifnull()` which are specifically designed for <<functions-null,dealing with null values>>.
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====
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This rule is the source of the famous (and controversial) _ternary logic_ of SQL.
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@ -215,6 +215,32 @@ See <<identification-variables>> and <<implicit-join>>.
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HQL has operators for working with strings, numeric values, and date/time types.
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The operator precedence is given by this table, from highest to lowest precedence:
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[cols="40,^20,~"]
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|===
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| Precedence class | Type | Operators
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| Grouping and tuple instantiation | | `( ... )` and `(x, y, z)`
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| Case lists | | `case ... end`
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| Member reference | Binary infix | `a.b`
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| Function application | Postfix | `f(x,y)`
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| Indexing | Postfix | `a[i]`
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| Unary numeric | Unary prefix | `+`, `-`
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| Duration conversions | Unary postfix | `by day` and friends
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| Binary multiplicative | Binary infix | `*`, `/`, `%`
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| Binary additive | Binary infix | `+`, `-`
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| Concatenation | Binary infix | `\|\|`
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| Nullness | Unary postfix | `is null`, `is empty`
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| Containment | Binary infix | `in`, `not in`
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| Between | Ternary infix | `between`, `not between`
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| Pattern matching | Binary infix | `like`, `ilike`, `not like`, `not ilike`
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| Existence | Unary prefix | `exists`
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| Membership | Binary infix | `member of`, `not member of`
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| Unary logical | Unary prefix | `not`
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| Binary logical | Binary infix | `and`, `or`
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|===
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[[concatenation]]
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==== String concatenation
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@ -494,7 +520,7 @@ The following functions make it easy to deal with null values:
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[discrete]
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===== Handling null values
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An abbreviated `case` expression that returns the first non-null operand.
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The `coalesce()` function is a sort of abbreviated `case` expression that returns the first non-null operand.
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[[coalesce-example]]
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[source, hql]
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@ -520,7 +546,7 @@ from Author as author
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[discrete]
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===== Producing null values
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Evaluates to null if its operands are equal, or to its first argument otherwise.
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On the other hand, `nullif()` evaluates to null if its operands are equal, or to its first argument otherwise.
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[[nullif-example]]
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[source, hql]
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@ -587,7 +613,7 @@ select year(created), month(created) from Order
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[discrete]
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===== Formatting dates and times
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This function formats a date, time, or datetime according to a pattern.
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The `format()` function formats a date, time, or datetime according to a pattern.
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The syntax is `format(datetime as pattern)`, and the pattern must be written in a subset of the pattern language defined by Java's `java.time.format.DateTimeFormatter`.
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@ -597,7 +623,7 @@ For a full list of `format()` pattern elements, see the Javadoc for https://docs
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[discrete]
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===== Truncating a date or time type
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This function truncates a date, time, or datetime to the temporal unit specified by field.
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The `truncate()` function truncates a date, time, or datetime to the temporal unit specified by field.
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The syntax is `truncate(datetime, field)`. Supported temporal units are: `year`, `month`, `day`, `hour`, `minute` or `second`.
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@ -651,8 +677,9 @@ Contrary to Java, positions of characters within strings are indexed from 1 inst
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[discrete]
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===== Concatenating strings
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Accepts a variable number of arguments, and produces a string by concatenating them.
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The JPQL-standard and ANSI SQL-standard `concat()` function accepts a variable number of arguments, and produces a string by concatenating them.
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[%unbreakable]
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[source, hql]
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----
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select concat(book.title, ' by ', listagg(author.name, ' & '))
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@ -663,6 +690,7 @@ group by book
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[discrete]
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===== Finding substrings
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The JPQL function `locate()` determines the position of a substring within another string.
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- The optional third argument is used to specify a position at which to start the search.
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@ -684,7 +712,8 @@ select position('Hibernate' in title) from Book
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[discrete]
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===== Slicing strings
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Returns a substring of the given string.
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Unsurprisingly, `substring()` returns a substring of the given string.
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- The second argument specifies the position of the first character of the substring.
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- The optional third argument specifies the maximum length of the substring.
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@ -788,7 +817,7 @@ The following functions apply to any identification variable that refers to a jo
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[discrete]
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===== Collection sizes
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The number of elements of a collection or to-many association.
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The `size()` function returns the number of elements of a collection or to-many association.
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[[size-example]]
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[source, hql]
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@ -800,13 +829,13 @@ select name, size(books) from Author
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[discrete]
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===== List elements and indexes
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A reference to an element or index of <<collection-valued-associations,joined list>>.
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The `element()` or `index()` function returns a reference to an element or index of a <<collection-valued-associations,joined list>>.
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[[map-functions]]
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[discrete]
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===== Map keys, values, and entries
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A reference to a key, value, or entry of a <<collection-valued-associations,joined map>>.
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The `key()`, `value()`, or `entry()` function returns a reference to a key, value, or entry of a <<collection-valued-associations,joined map>>.
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[[elements-indices]]
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==== Quantification over collections
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@ -873,7 +902,7 @@ There are several ways to call native or user-defined SQL functions.
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[TIP]
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====
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Registering a function isn't hard, but is beyond the scope of this chapter.
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Registering a function isn't hard, but is beyond the scope of this guide.
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(It's even possible to use the APIs Hibernate provides to make your own _portable_ functions!)
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====
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@ -1095,8 +1124,9 @@ from Book as book
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where :edition in elements(book.editions)
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----
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This example doesn't work on every database:
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The next example doesn't work on every database:
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[%unbreakable]
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[source, hql]
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----
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from Author as author
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@ -1106,6 +1136,7 @@ where (author.person.name, author.person.birthdate)
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Here we used a "row value" constructor, a seemingly pretty basic feature which is surprisingly-poorly supported.
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[%unbreakable]
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[TIP]
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====
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Here's a very useful idiom:
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