From e001b622cd39122a14abed794a1da40f0b752858 Mon Sep 17 00:00:00 2001 From: Gavin Date: Mon, 29 May 2023 20:35:19 +0200 Subject: [PATCH] add table of operator precedence to HQL guide --- .../main/asciidoc/querylanguage/Concepts.adoc | 2 +- .../asciidoc/querylanguage/Expressions.adoc | 53 +++++++++++++++---- 2 files changed, 43 insertions(+), 12 deletions(-) diff --git a/documentation/src/main/asciidoc/querylanguage/Concepts.adoc b/documentation/src/main/asciidoc/querylanguage/Concepts.adoc index b9c3f1f0f9..8e5521fa9d 100644 --- a/documentation/src/main/asciidoc/querylanguage/Concepts.adoc +++ b/documentation/src/main/asciidoc/querylanguage/Concepts.adoc @@ -191,7 +191,7 @@ But in SQL, and therefore also in HQL and JPQL, such an expression evaluates to It's almost always the case that an operation applied to a null value yields another null value. This applies to function application, to operators like `*` and `||`, to comparison operators like `<` and `=`, and even to logical operations like `and` and `not`. -The exceptions to this rule are the functions `coalesce()` and `ifnull()` which are specifically designed for <>. +The exceptions to this rule are the `is null` operator and the functions `coalesce()` and `ifnull()` which are specifically designed for <>. ==== This rule is the source of the famous (and controversial) _ternary logic_ of SQL. diff --git a/documentation/src/main/asciidoc/querylanguage/Expressions.adoc b/documentation/src/main/asciidoc/querylanguage/Expressions.adoc index 77de0a7d34..fa004df9c7 100644 --- a/documentation/src/main/asciidoc/querylanguage/Expressions.adoc +++ b/documentation/src/main/asciidoc/querylanguage/Expressions.adoc @@ -215,6 +215,32 @@ See <> and <>. HQL has operators for working with strings, numeric values, and date/time types. +The operator precedence is given by this table, from highest to lowest precedence: + +[cols="40,^20,~"] +|=== +| Precedence class | Type | Operators + +| Grouping and tuple instantiation | | `( ... )` and `(x, y, z)` +| Case lists | | `case ... end` +| Member reference | Binary infix | `a.b` +| Function application | Postfix | `f(x,y)` +| Indexing | Postfix | `a[i]` +| Unary numeric | Unary prefix | `+`, `-` +| Duration conversions | Unary postfix | `by day` and friends +| Binary multiplicative | Binary infix | `*`, `/`, `%` +| Binary additive | Binary infix | `+`, `-` +| Concatenation | Binary infix | `\|\|` +| Nullness | Unary postfix | `is null`, `is empty` +| Containment | Binary infix | `in`, `not in` +| Between | Ternary infix | `between`, `not between` +| Pattern matching | Binary infix | `like`, `ilike`, `not like`, `not ilike` +| Existence | Unary prefix | `exists` +| Membership | Binary infix | `member of`, `not member of` +| Unary logical | Unary prefix | `not` +| Binary logical | Binary infix | `and`, `or` +|=== + [[concatenation]] ==== String concatenation @@ -494,7 +520,7 @@ The following functions make it easy to deal with null values: [discrete] ===== Handling null values -An abbreviated `case` expression that returns the first non-null operand. +The `coalesce()` function is a sort of abbreviated `case` expression that returns the first non-null operand. [[coalesce-example]] [source, hql] @@ -520,7 +546,7 @@ from Author as author [discrete] ===== Producing null values -Evaluates to null if its operands are equal, or to its first argument otherwise. +On the other hand, `nullif()` evaluates to null if its operands are equal, or to its first argument otherwise. [[nullif-example]] [source, hql] @@ -587,7 +613,7 @@ select year(created), month(created) from Order [discrete] ===== Formatting dates and times -This function formats a date, time, or datetime according to a pattern. +The `format()` function formats a date, time, or datetime according to a pattern. 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`. @@ -597,7 +623,7 @@ For a full list of `format()` pattern elements, see the Javadoc for https://docs [discrete] ===== Truncating a date or time type -This function truncates a date, time, or datetime to the temporal unit specified by field. +The `truncate()` function truncates a date, time, or datetime to the temporal unit specified by field. The syntax is `truncate(datetime, field)`. Supported temporal units are: `year`, `month`, `day`, `hour`, `minute` or `second`. @@ -651,8 +677,9 @@ Contrary to Java, positions of characters within strings are indexed from 1 inst [discrete] ===== Concatenating strings -Accepts a variable number of arguments, and produces a string by concatenating them. +The JPQL-standard and ANSI SQL-standard `concat()` function accepts a variable number of arguments, and produces a string by concatenating them. +[%unbreakable] [source, hql] ---- select concat(book.title, ' by ', listagg(author.name, ' & ')) @@ -663,6 +690,7 @@ group by book [discrete] ===== Finding substrings + The JPQL function `locate()` determines the position of a substring within another string. - The optional third argument is used to specify a position at which to start the search. @@ -684,7 +712,8 @@ select position('Hibernate' in title) from Book [discrete] ===== Slicing strings -Returns a substring of the given string. + +Unsurprisingly, `substring()` returns a substring of the given string. - The second argument specifies the position of the first character of the substring. - The optional third argument specifies the maximum length of the substring. @@ -788,7 +817,7 @@ The following functions apply to any identification variable that refers to a jo [discrete] ===== Collection sizes -The number of elements of a collection or to-many association. +The `size()` function returns the number of elements of a collection or to-many association. [[size-example]] [source, hql] @@ -800,13 +829,13 @@ select name, size(books) from Author [discrete] ===== List elements and indexes -A reference to an element or index of <>. +The `element()` or `index()` function returns a reference to an element or index of a <>. [[map-functions]] [discrete] ===== Map keys, values, and entries -A reference to a key, value, or entry of a <>. +The `key()`, `value()`, or `entry()` function returns a reference to a key, value, or entry of a <>. [[elements-indices]] ==== Quantification over collections @@ -873,7 +902,7 @@ There are several ways to call native or user-defined SQL functions. [TIP] ==== -Registering a function isn't hard, but is beyond the scope of this chapter. +Registering a function isn't hard, but is beyond the scope of this guide. (It's even possible to use the APIs Hibernate provides to make your own _portable_ functions!) ==== @@ -1095,8 +1124,9 @@ from Book as book where :edition in elements(book.editions) ---- -This example doesn't work on every database: +The next example doesn't work on every database: +[%unbreakable] [source, hql] ---- from Author as author @@ -1106,6 +1136,7 @@ where (author.person.name, author.person.birthdate) Here we used a "row value" constructor, a seemingly pretty basic feature which is surprisingly-poorly supported. +[%unbreakable] [TIP] ==== Here's a very useful idiom: