fix: EXPOSED-1040 Support SELECT without FROM table clause

[Leonid Stashevsky (e5l)]

Description

Introduce select expression which allows to use select statement without column set.

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Type of Change

Please mark the relevant options with an "X":

• Bug fix
• New feature
• Documentation update

Updates/remove existing public API methods:

• Is breaking change

Affected databases:

• MariaDB
• Mysql5
• Mysql8
• Oracle
• Postgres
• Redshift
• SqlServer
• H2
• SQLite

Checklist

• Unit tests are in place
• The build is green (including the Detekt check)
• All public methods affected by my PR has up to date API docs
• Documentation for my change is up to date

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Related Issues

EXPOSED-1040 Support SELECT without FROM table clause

[Copilot]

Pull request overview

Adds first-class support for “tableless” SELECT statements (i.e., SELECT 1 without an explicit FROM) across Exposed’s JDBC and R2DBC APIs, including convenience terminals for fetching a single projected value and documentation/tests to lock in the behavior.

Changes:

• Introduces top-level tableless select(...) overloads (JDBC + R2DBC) backed by Table.Dual, plus selectValue(...) terminals.
• Adds a generic literal(value) helper in exposed-core for wrapping common scalar Kotlin/Java values as SQL literals, plus tests.
• Updates user documentation and changelog; refreshes SQL Server docker image tag used in dev/test infra.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
exposed-tests/src/test/kotlin/org/jetbrains/exposed/v1/tests/shared/types/LiteralOpTests.kt	New tests for literal(value) type resolution, decimal precision/scale, and unsupported types.
exposed-tests/src/test/kotlin/org/jetbrains/exposed/v1/tests/shared/dml/SelectExpressionTest.kt	New JDBC tests covering tableless selects, selectValue, set ops, derived table usage, and edge cases.
exposed-tests/src/test/kotlin/org/jetbrains/exposed/v1/tests/shared/dml/DualTableTest.kt	Removes old Table.Dual-focused test, superseded by tableless select tests.
exposed-r2dbc/src/main/kotlin/org/jetbrains/exposed/v1/r2dbc/Queries.kt	Adds tableless select(...) overloads and suspending selectValue(...) terminals for R2DBC.
exposed-r2dbc/api/exposed-r2dbc.api	Public API surface update for the new R2DBC query helpers.
exposed-r2dbc-tests/src/test/kotlin/org/jetbrains/exposed/v1/r2dbc/sql/tests/shared/dml/SelectExpressionTest.kt	New R2DBC tests validating tableless select and selectValue behavior.
exposed-r2dbc-tests/src/test/kotlin/org/jetbrains/exposed/v1/r2dbc/sql/tests/shared/dml/DualTableTest.kt	Removes old R2DBC Table.Dual test, superseded by tableless select tests.
exposed-jdbc/src/main/kotlin/org/jetbrains/exposed/v1/jdbc/Queries.kt	Adds tableless select(...) overloads and selectValue(...) terminals for JDBC.
exposed-jdbc/api/exposed-jdbc.api	Public API surface update for the new JDBC query helpers.
exposed-core/src/main/kotlin/org/jetbrains/exposed/v1/core/LiteralOp.kt	Adds literal(value) auto-resolver for common scalar types (+ UUID support).
exposed-core/src/main/kotlin/org/jetbrains/exposed/v1/core/BinaryLiteralColumnType.kt	Internal column type to render ByteArray literals using blob/hex formatting rules.
exposed-core/api/exposed-core.api	Public API surface update for the new literal(value) function.
documentation-website/Writerside/topics/DSL-Querying-data.topic	Adds a “Tableless SELECT queries” documentation chapter with examples and caveats.
CHANGELOG.md	Adds feature entry describing tableless select + selectValue + literal.
buildScripts/docker/docker-compose-sqlserver.yml	Updates SQL Server container image tag.

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[Chantal Loncle (bog-walk)]

Please also check failing tests on some db?

[Chantal Loncle (bog-walk)]

It makes sense for a test that relies solely on exposed-core to only have a single (JDBC) test suite.
Please still tag it using something like @Tag(NOT_APPLICABLE_TO_R2DBC) so we know why there is a test number discrepancy between JDBC & R2DBC (and why it doesn't need to be added).

[Chantal Loncle (bog-walk)]

No issue with this class except I do wonder how differently the output is compared to what we already have. There is a current top-level .asLiteral() that returns a LiteralOp and it also has a special branch for ByteArray + BasicBinaryColumnType --> source code

Would literal(byteArrayOf(0x01, 0x7F)) provide the same result as column.asLiteral(byteArrayOf(0x01, 0x7F))?
I haven't checked, just wondering, but hopefully it does?

[Leonid Stashevsky (e5l)]

it's interesting that we preferred the string literal, let me explore

[Leonid Stashevsky (e5l)]

The existing asLiteral works not correct when the non-utf8 bytes are present in the array. Here is the simple test:

@Test
fun testBinaryDefaultPreservesNonUtf8Bytes() {
    val expected = byteArrayOf(0x89.toByte(), 0x50, 0x4E, 0x47)
    val table = object : Table("binary_default_test") {
        val payload = binary("payload").default(expected)
    }

    withTables(table) {
        table.insert {}

        val actual = table.selectAll().single()[table.payload]
        assertContentEquals(expected, actual)
    }
}

It follows the path default(bytes) -> asLiteral(bytes) -> dbDefaultToString(...). I will update the asLiteral to also follow hex serialization instead of utf-8