diff --git a/src/test/kotlin/kestrel/ExpressionLanguageTest.kt b/src/test/kotlin/kestrel/ExpressionLanguageTest.kt
new file mode 100644
index 0000000..cecce8e
--- /dev/null
+++ b/src/test/kotlin/kestrel/ExpressionLanguageTest.kt
@@ -0,0 +1,158 @@
+package kestrel
+
+import java.math.BigDecimal
+import java.time.LocalDate
+import kestrel.catalog.Catalog
+import kestrel.engine.Executor
+import kestrel.engine.ExplainResult
+import kestrel.engine.SelectResult
+import kestrel.engine.StatementResult
+import kestrel.sql.lexer.Lexer
+import kestrel.sql.parser.Parser
+import kestrel.storage.Value
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+import kotlin.test.assertTrue
+
+class ExpressionLanguageTest {
+    private val catalog = Catalog()
+    private val executor = Executor(catalog)
+
+    private fun run(sql: String): List<StatementResult> =
+        Parser(Lexer(sql).tokenize()).parseProgram().map { executor.execute(it) }
+
+    private fun select(sql: String): SelectResult = run(sql).single() as SelectResult
+
+    private fun int(value: Long) = Value.IntegerValue(value)
+    private fun text(value: String) = Value.TextValue(value)
+
+    private fun seedUsers() {
+        run("CREATE TABLE users (id INTEGER PRIMARY KEY, name TEXT NOT NULL, age INTEGER, bio TEXT)")
+        run(
+            "INSERT INTO users VALUES " +
+                "(1, 'ada', 36, 'mathematician'), (2, 'linus', 54, NULL), " +
+                "(3, 'grace', 85, 'rear admiral')"
+        )
+    }
+
+    @Test
+    fun scalarFunctionInProjection() {
+        seedUsers()
+        val result = select("SELECT UPPER(name) FROM users ORDER BY id ASC")
+        assertEquals(listOf("upper"), result.columns)
+        assertEquals(listOf(text("ADA"), text("LINUS"), text("GRACE")), result.rows.map { it[0] })
+    }
+
+    @Test
+    fun scalarFunctionInWhereClause() {
+        seedUsers()
+        val result = select("SELECT name FROM users WHERE LENGTH(name) > 4 ORDER BY name ASC")
+        assertEquals(listOf(listOf(text("grace")), listOf(text("linus"))), result.rows)
+    }
+
+    @Test
+    fun scalarFunctionUsableInUpdateAssignment() {
+        seedUsers()
+        run("UPDATE users SET name = UPPER(name) WHERE id = 1")
+        val result = select("SELECT name FROM users WHERE id = 1")
+        assertEquals(listOf(listOf(text("ADA"))), result.rows)
+    }
+
+    @Test
+    fun nestedFunctionCalls() {
+        seedUsers()
+        val result = select("SELECT SUBSTR(UPPER(name), 1, 1) FROM users WHERE id = 1")
+        assertEquals(listOf(listOf(text("A"))), result.rows)
+    }
+
+    @Test
+    fun isNullFiltersRowsWithMissingValues() {
+        seedUsers()
+        val result = select("SELECT name FROM users WHERE bio IS NULL")
+        assertEquals(listOf(listOf(text("linus"))), result.rows)
+        val negated = select("SELECT COUNT(*) FROM users WHERE bio IS NOT NULL")
+        assertEquals(listOf(listOf(int(2))), negated.rows)
+    }
+
+    @Test
+    fun inClauseMatchesAgainstLiteralSet() {
+        seedUsers()
+        val result = select("SELECT name FROM users WHERE age IN (36, 85) ORDER BY age ASC")
+        assertEquals(listOf(listOf(text("ada")), listOf(text("grace"))), result.rows)
+    }
+
+    @Test
+    fun notInExcludesMatchingRows() {
+        seedUsers()
+        val result = select("SELECT name FROM users WHERE age NOT IN (36, 85)")
+        assertEquals(listOf(listOf(text("linus"))), result.rows)
+    }
+
+    @Test
+    fun betweenSelectsInclusiveRange() {
+        seedUsers()
+        val result = select("SELECT name FROM users WHERE age BETWEEN 40 AND 90 ORDER BY age ASC")
+        assertEquals(listOf(listOf(text("linus")), listOf(text("grace"))), result.rows)
+    }
+
+    @Test
+    fun likeMatchesWildcardPattern() {
+        seedUsers()
+        val result = select("SELECT name FROM users WHERE bio LIKE '%admiral' ")
+        assertEquals(listOf(listOf(text("grace"))), result.rows)
+    }
+
+    @Test
+    fun caseExpressionInProjection() {
+        seedUsers()
+        val result = select(
+            "SELECT name, CASE WHEN age < 50 THEN 'young' WHEN age < 80 THEN 'mid' ELSE 'senior' END " +
+                "FROM users ORDER BY id ASC"
+        )
+        assertEquals(
+            listOf(
+                listOf(text("ada"), text("young")),
+                listOf(text("linus"), text("mid")),
+                listOf(text("grace"), text("senior"))
+            ),
+            result.rows
+        )
+    }
+
+    @Test
+    fun caseExpressionUsableInWhereClause() {
+        seedUsers()
+        val result = select(
+            "SELECT name FROM users WHERE CASE WHEN age > 40 THEN TRUE ELSE FALSE END ORDER BY name ASC"
+        )
+        assertEquals(listOf(listOf(text("grace")), listOf(text("linus"))), result.rows)
+    }
+
+    @Test
+    fun combiningPredicatesWithLogicalOperators() {
+        seedUsers()
+        val result = select(
+            "SELECT name FROM users WHERE age BETWEEN 30 AND 60 AND name LIKE 'a%'"
+        )
+        assertEquals(listOf(listOf(text("ada"))), result.rows)
+    }
+
+    @Test
+    fun aggregateOfScalarFunctionResult() {
+        seedUsers()
+        val result = select("SELECT SUM(LENGTH(name)) FROM users")
+        assertEquals(listOf(listOf(int(3 + 5 + 5))), result.rows)
+    }
+
+    @Test
+    fun groupByWithFunctionOnGroupedColumn() {
+        run("CREATE TABLE t (category TEXT, amount INTEGER)")
+        run("INSERT INTO t VALUES ('Eng', 10), ('eng', 20), ('Ops', 5)")
+        val result = select("SELECT LOWER(category), SUM(amount) FROM t GROUP BY LOWER(category) ORDER BY LOWER(category) ASC")
+        assertEquals(
+            listOf(listOf(text("eng"), int(30)), listOf(text("ops"), int(5))),
+            result.rows
+        )
+    }
+