fix: support character set introduced string literals

src/main/jjtree/net/sf/jsqlparser/parser/JSqlParserCC.jjt

@@ -301,6 +301,19 @@ public class CCJSqlParser extends AbstractJSqlParser<CCJSqlParser> {
         }
     }
 
+    /**
+     * Whether the next two tokens form a character-set-introduced string literal,
+     * for example {@code _utf8mb4'text'} or {@code _ISO8859_1 'text'}.
+     */
+    private boolean isCharacterSetIntroducedStringAhead() {
+        Token introducer = getToken(1);
+        Token literal = getToken(2);
+        return introducer.kind == S_IDENTIFIER
+                && introducer.image != null
+                && introducer.image.length() > 1
+                && introducer.image.charAt(0) == '_'
+                && literal.kind == S_CHAR_LITERAL;
+    }
 
     /**
      * Tokens that have dedicated branches in PrimaryExpression AFTER the Function branch.
@@ -8067,6 +8080,18 @@ Expression SimpleExpression():
     }
 }
 
+StringValue CharacterSetIntroducedString():
+{
+    Token introducer;
+    Token literal;
+}
+{
+    introducer=<S_IDENTIFIER> literal=<S_CHAR_LITERAL>
+    {
+        return new StringValue(literal.image).withPrefix(introducer.image);
+    }
+}
+
 /** Multiplicative/bitwise-shift — higher precedence */
 Expression MulChain():
 {
@@ -8243,6 +8268,9 @@ Expression PrimaryExpression() #PrimaryExpression:
 
         | LOOKAHEAD(2, {!interrupted}) <K_ALL> { retval = new AllValue(); }
 
+        | LOOKAHEAD({ !interrupted && isCharacterSetIntroducedStringAhead() })
+                  retval=CharacterSetIntroducedString()
+
         | LOOKAHEAD(2, {!interrupted}) retval=Column()
             [
                 LOOKAHEAD( "(" "+" ")" ("," | ")") )

src/test/java/net/sf/jsqlparser/statement/select/SelectTest.java

@@ -36,6 +36,7 @@
 import net.sf.jsqlparser.expression.Alias;
 import net.sf.jsqlparser.expression.AllValue;
 import net.sf.jsqlparser.expression.BinaryExpression;
+import net.sf.jsqlparser.expression.CollateExpression;
 import net.sf.jsqlparser.expression.DoubleValue;
 import net.sf.jsqlparser.expression.Expression;
 import net.sf.jsqlparser.expression.Function;
@@ -4183,6 +4184,38 @@ public void testEscaped() throws JSQLParserException {
         assertSqlCanBeParsedAndDeparsed("SELECT _utf8'testvalue'");
     }
 
+    @ParameterizedTest
+    @ValueSource(strings = {"_utf8mb4'testvalue'", "_utf8mb4 'testvalue'",
+            "_utf8 'testvalue'", "_latin1'testvalue'", "_binary'testvalue'",
+            "_ISO8859_1 'testvalue'"})
+    public void testCharacterSetIntroducedString(String expression) throws JSQLParserException {
+        Select select = (Select) CCJSqlParserUtil.parse("SELECT " + expression);
+        SelectItem<?> selectItem = select.getPlainSelect().getSelectItem(0);
+        StringValue stringValue = assertInstanceOf(StringValue.class, selectItem.getExpression());
+
+        assertEquals(expression.substring(0, expression.indexOf('\'')).trim(),
+                stringValue.getPrefix());
+        assertEquals("testvalue", stringValue.getValue());
+        assertNull(selectItem.getAlias());
+    }
+
+    @Test
+    public void testCharacterSetIntroducedStringWithCollate() throws JSQLParserException {
+        String sql = "SELECT _utf8mb4'some text' COLLATE utf8mb4_unicode_ci AS custom_string";
+        Select select = (Select) CCJSqlParserUtil.parse(sql);
+        SelectItem<?> selectItem = select.getPlainSelect().getSelectItem(0);
+        CollateExpression collateExpression =
+                assertInstanceOf(CollateExpression.class, selectItem.getExpression());
+        StringValue stringValue = assertInstanceOf(StringValue.class,
+                collateExpression.getLeftExpression());
+
+        assertEquals("_utf8mb4", stringValue.getPrefix());
+        assertEquals("some text", stringValue.getValue());
+        assertEquals("utf8mb4_unicode_ci", collateExpression.getCollate());
+        assertEquals("custom_string", selectItem.getAlias().getName());
+        assertEquals(sql, select.toString());
+    }
+
     @Test
     public void testIssue563MultiSubJoin() throws JSQLParserException {
         assertSqlCanBeParsedAndDeparsed(