Add support for REFRESH clause in CREATE MATERIALIZED VIEW (#121)

Parse and explain REFRESH AFTER/EVERY interval APPEND TO syntax:
- Add REFRESH-related fields to CreateQuery AST
- Parse REFRESH type (AFTER/EVERY), interval, unit, APPEND TO, and EMPTY
- Output "Refresh strategy definition" and "TimeInterval" in explain

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: kyleconroy

ast/ast.go

@@ -278,6 +278,12 @@ type CreateQuery struct {
 	ToDatabase       string               `json:"to_database,omitempty"` // Target database for materialized views
 	To               string               `json:"to,omitempty"`          // Target table for materialized views
 	Populate         bool                 `json:"populate,omitempty"`    // POPULATE for materialized views
+	HasRefresh       bool                 `json:"has_refresh,omitempty"` // Has REFRESH clause
+	RefreshType      string               `json:"refresh_type,omitempty"` // AFTER or EVERY
+	RefreshInterval  Expression           `json:"refresh_interval,omitempty"` // Interval value
+	RefreshUnit      string               `json:"refresh_unit,omitempty"` // SECOND, MINUTE, etc.
+	RefreshAppend    bool                 `json:"refresh_append,omitempty"` // APPEND TO was specified
+	Empty            bool                 `json:"empty,omitempty"`       // EMPTY keyword was specified
 	Columns          []*ColumnDeclaration `json:"columns,omitempty"`
 	Indexes          []*IndexDefinition   `json:"indexes,omitempty"`
 	Projections      []*Projection        `json:"projections,omitempty"`

internal/explain/statements.go

@@ -237,6 +237,10 @@ func explainCreateQuery(sb *strings.Builder, n *ast.CreateQuery, indent string,
 	if len(n.QuerySettings) > 0 {
 		children++
 	}
+	// Count REFRESH strategy as a child
+	if n.HasRefresh {
+		children++ // Refresh strategy definition
+	}
 	// For materialized views with TO clause but no storage, count ViewTargets as a child
 	if n.Materialized && n.To != "" && !hasStorageChild {
 		children++ // ViewTargets
@@ -353,6 +357,11 @@ func explainCreateQuery(sb *strings.Builder, n *ast.CreateQuery, indent string,
 			}
 		}
 	}
+	// Output REFRESH strategy for materialized views with REFRESH clause
+	if n.HasRefresh {
+		fmt.Fprintf(sb, "%s Refresh strategy definition (children 1)\n", indent)
+		fmt.Fprintf(sb, "%s  TimeInterval\n", indent)
+	}
 	// For materialized views, output AsSelect before storage definition
 	if n.Materialized && n.AsSelect != nil {
 		// Set context flag to prevent Format from being output at SelectWithUnionQuery level

parser/parser.go

@@ -2826,6 +2826,72 @@ func (p *Parser) parseCreateView(create *ast.CreateQuery) {
 		}
 	}
 
+	// Handle REFRESH clause for materialized views (REFRESH AFTER/EVERY interval APPEND TO target)
+	if p.currentIs(token.IDENT) && strings.ToUpper(p.current.Value) == "REFRESH" {
+		p.nextToken() // skip REFRESH
+		create.HasRefresh = true
+
+		// Parse refresh timing: AFTER interval or EVERY interval
+		if p.currentIs(token.IDENT) {
+			upper := strings.ToUpper(p.current.Value)
+			if upper == "AFTER" || upper == "EVERY" {
+				create.RefreshType = upper
+				p.nextToken()
+				// Parse interval value and unit
+				create.RefreshInterval = p.parseExpression(AND_PREC)
+				// Parse interval unit if present as identifier
+				if p.currentIs(token.IDENT) {
+					unitUpper := strings.ToUpper(p.current.Value)
+					if unitUpper == "SECOND" || unitUpper == "MINUTE" || unitUpper == "HOUR" ||
+						unitUpper == "DAY" || unitUpper == "WEEK" || unitUpper == "MONTH" || unitUpper == "YEAR" {
+						create.RefreshUnit = unitUpper
+						p.nextToken()
+					}
+				}
+			}
+		}
+
+		// Handle APPEND TO target - different from regular TO, part of REFRESH strategy
+		if p.currentIs(token.IDENT) && strings.ToUpper(p.current.Value) == "APPEND" {
+			p.nextToken() // skip APPEND
+			create.RefreshAppend = true
+			if p.currentIs(token.TO) {
+				p.nextToken() // skip TO
+				toName := p.parseIdentifierName()
+				if p.currentIs(token.DOT) {
+					p.nextToken()
+					create.ToDatabase = toName
+					create.To = p.parseIdentifierName()
+				} else {
+					create.To = toName
+				}
+			}
+		}
+
+		// For REFRESH ... APPEND TO target (columns), column definitions come after
+		if p.currentIs(token.LPAREN) && len(create.Columns) == 0 {
+			p.nextToken()
+			for !p.currentIs(token.RPAREN) && !p.currentIs(token.EOF) {
+				col := p.parseColumnDeclaration()
+				if col != nil {
+					create.Columns = append(create.Columns, col)
+				}
+				if p.currentIs(token.COMMA) {
+					p.nextToken()
+				} else {
+					break
+				}
+			}
+			p.expect(token.RPAREN)
+		}
+
+		// Handle EMPTY keyword
+		if p.currentIs(token.IDENT) && strings.ToUpper(p.current.Value) == "EMPTY" {
+			create.Empty = true
+			p.nextToken()
+		}
+	}
+
 	// Parse column definitions (e.g., CREATE VIEW v (x UInt64) AS SELECT ...)
 	// For MATERIALIZED VIEW, this can also include INDEX, PROJECTION, and PRIMARY KEY
 	if p.currentIs(token.LPAREN) {

parser/testdata/00950_test_double_delta_codec_types/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt17": true
-  }
-}
+{}