fix: resolve all synq_clickhouse and synq_postgres corpus failures

CLAUDE.md

@@ -107,7 +107,10 @@ node scripts/compare-corpus-reports.js target/corpus-report.json target/corpus-r
 - Handles panics and stack overflows gracefully
 - Same binary used in GitHub Actions (`.github/workflows/corpus.yml`)
 - Can be used for profiling (same workload as tests)
-- `customer_*` dialect prefixes automatically stripped (customer_bigquery → bigquery)
+- `customer_*` and `synq_*` dialect prefixes automatically stripped (customer_bigquery → bigquery, synq_clickhouse → clickhouse)
+- **Cannot run corpus-runner on subdirectories** — dialect is extracted from first path component relative to corpus root
+- **Corpus files are symlinked** from `kernel-cll-corpus` repo — commit corpus changes there, not in sqlparser-rs
+- Analyze failures: parse `target/corpus-report.json` with Python to filter/group `test_results` by dialect or error pattern
 
 **Development workflow:**
 - Use corpus-runner for fast feedback (6.7s vs 2+ hours)
@@ -245,6 +248,11 @@ Semantic analysis varies drastically between SQL dialects and is left to consume
 3. **Add Tests**: Write dialect-specific tests in appropriate test file
 4. **Consider Dialect**: Use `dialect_of!` if syntax is dialect-specific
 
+#### Adding New Keywords
+Keywords in `src/keywords.rs` MUST be in strict alphabetical order — `ALL_KEYWORDS` uses binary search.
+If a keyword is out of order, the tokenizer silently fails to recognize it (maps to `Keyword::NoKeyword`).
+Verify ordering carefully: e.g., `EXCHANGE` < `EXCLUDE` < `EXEC` (compare character by character).
+
 #### AST Change Workflow
 When adding fields to AST structs, you must update ALL pattern matches:
 1. Add field to struct definition (e.g., `src/ast/mod.rs`, `src/ast/query.rs`)

src/ast/ddl.rs

@@ -26,8 +26,8 @@ use sqlparser_derive::{Visit, VisitMut};
 
 use crate::ast::value::escape_single_quote_string;
 use crate::ast::{
-    display_comma_separated, display_separated, DataType, Expr, Ident, ObjectName, OrderBy, Select,
-    SequenceOptions,
+    display_comma_separated, display_separated, Assignment, DataType, Expr, Ident, ObjectName,
+    OrderBy, Select, SequenceOptions,
 };
 use crate::tokenizer::Token;
 
@@ -158,6 +158,45 @@ pub enum AlterTableOperation {
     /// Note: this is a ClickHouse-specific operation
     /// <https://clickhouse.com/docs/sql-reference/statements/alter/projection>
     DropProjection { if_exists: bool, name: Ident },
+
+    /// `MODIFY COLUMN <column_name> <data_type> [<options>]`
+    ///
+    /// Note: this is a ClickHouse-specific operation
+    /// <https://clickhouse.com/docs/en/sql-reference/statements/alter/column#modify-column>
+    ModifyColumn {
+        column_name: Ident,
+        /// Data type is optional (e.g., `MODIFY COLUMN x REMOVE DEFAULT` has no type)
+        column_type: Option<DataType>,
+        /// Optional column options (e.g., DEFAULT, REMOVE DEFAULT, etc.)
+        options: Vec<ColumnOption>,
+    },
+
+    /// `MATERIALIZE COLUMN <column_name>`
+    ///
+    /// Note: this is a ClickHouse-specific operation
+    /// <https://clickhouse.com/docs/en/sql-reference/statements/alter/column#materialize-column>
+    MaterializeColumn { column_name: Ident },
+
+    /// `MATERIALIZE PROJECTION <projection_name>`
+    ///
+    /// Note: this is a ClickHouse-specific operation
+    /// <https://clickhouse.com/docs/sql-reference/statements/alter/projection>
+    MaterializeProjection { name: Ident },
+
+    /// `DROP INDEX [IF EXISTS] <index_name>`
+    ///
+    /// Note: this is a ClickHouse-specific operation
+    /// <https://clickhouse.com/docs/en/sql-reference/statements/alter/index#drop-index>
+    DropIndex { if_exists: bool, name: Ident },
+
+    /// `UPDATE <column> = <expr> [, ...] WHERE <condition>`
+    ///
+    /// Note: this is a ClickHouse-specific operation (lightweight mutation)
+    /// <https://clickhouse.com/docs/en/sql-reference/statements/alter/update>
+    UpdateData {
+        assignments: Vec<Assignment>,
+        selection: Option<Expr>,
+    },
 }
 
 #[derive(Debug, Clone, PartialEq, PartialOrd, Eq, Ord, Hash)]
@@ -314,6 +353,43 @@ impl fmt::Display for AlterTableOperation {
                 }
                 write!(f, " {name}")
             }
+            AlterTableOperation::ModifyColumn {
+                column_name,
+                column_type,
+                options,
+            } => {
+                write!(f, "MODIFY COLUMN {column_name}")?;
+                if let Some(dt) = column_type {
+                    write!(f, " {dt}")?;
+                }
+                for option in options {
+                    write!(f, " {option}")?;
+                }
+                Ok(())
+            }
+            AlterTableOperation::MaterializeColumn { column_name } => {
+                write!(f, "MATERIALIZE COLUMN {column_name}")
+            }
+            AlterTableOperation::MaterializeProjection { name } => {
+                write!(f, "MATERIALIZE PROJECTION {name}")
+            }
+            AlterTableOperation::DropIndex { if_exists, name } => {
+                write!(f, "DROP INDEX")?;
+                if *if_exists {
+                    write!(f, " IF EXISTS")?;
+                }
+                write!(f, " {name}")
+            }
+            AlterTableOperation::UpdateData {
+                assignments,
+                selection,
+            } => {
+                write!(f, "UPDATE {}", display_comma_separated(assignments))?;
+                if let Some(predicate) = selection {
+                    write!(f, " WHERE {predicate}")?;
+                }
+                Ok(())
+            }
         }
     }
 }

src/ast/mod.rs

@@ -1951,6 +1951,16 @@ pub enum Statement {
         name: Ident,
         operation: AlterRoleOperation,
     },
+    /// `EXCHANGE TABLES <table1> AND <table2>`
+    ///
+    /// Note: this is a ClickHouse-specific statement
+    /// <https://clickhouse.com/docs/en/sql-reference/statements/exchange>
+    ExchangeTables {
+        #[cfg_attr(feature = "visitor", visit(with = "visit_relation"))]
+        first: ObjectName,
+        #[cfg_attr(feature = "visitor", visit(with = "visit_relation"))]
+        second: ObjectName,
+    },
     /// DROP
     Drop {
         /// The type of the object to drop: TABLE, VIEW, etc.
@@ -3539,6 +3549,9 @@ impl fmt::Display for Statement {
                     operations = display_comma_separated(operations)
                 )
             }
+            Statement::ExchangeTables { first, second } => {
+                write!(f, "EXCHANGE TABLES {first} AND {second}")
+            }
             Statement::AlterIndex { name, operation } => {
                 write!(f, "ALTER INDEX {name} {operation}")
             }

src/keywords.rs

@@ -281,6 +281,7 @@ define_keywords!(
     EVENT,
     EVERY,
     EXCEPT,
+    EXCHANGE,
     EXCLUDE,
     EXEC,
     EXECUTE,
@@ -437,6 +438,7 @@ define_keywords!(
     MATCHED,
     MATCH_CONDITION,
     MATCH_RECOGNIZE,
+    MATERIALIZE,
     MATERIALIZED,
     MAX,
     MAXVALUE,
@@ -460,6 +462,7 @@ define_keywords!(
     MODE,
     MODEL,
     MODIFIES,
+    MODIFY,
     MODULE,
     MONTH,
     MONTHS,
@@ -595,6 +598,7 @@ define_keywords!(
     RELATIVE,
     RELEASE,
     RELY,
+    REMOVE,
     RENAME,
     REORG,
     REPAIR,