asereda-gs commented on a change in pull request #1095: [CALCITE-2599] add the
ASCII function
URL: https://github.com/apache/calcite/pull/1095#discussion_r264004647
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File path: core/src/main/java/org/apache/calcite/runtime/SqlFunctions.java
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@@ -237,6 +238,12 @@ public static String initcap(String s) {
return newS.toString();
}
+ /** SQL ASCII(string) function. */
+ public static int ascii(String s) {
+ return s.length() == 0
+ ? 0 : s.substring(0, 1).getBytes(StandardCharsets.UTF_8)[0];
Review comment:
I did a little test:
```java
@Test
public void basic() {
final char[] chars = {0x00, 0x1B,
'A', 'a', '0', '{', '}',
'\n', '\r', '\t', ' ',
0x80, 0x99,
'\u0391', '\u03A9', '\u0391'};
for (char ch: chars) {
final String value = String.valueOf(ch);
assertEquals(String.format("for %s (ascii:%d hex:0x%02X)", value,
(int) ch, (int) ch),
ascii1(value), ascii2(value));
}
}
private static int ascii1(String str) {
return str.isEmpty() ? 0 : str.getBytes(StandardCharsets.UTF_8)[0];
}
private static int ascii2(String str) {
return str.isEmpty() ? 0 : str.charAt(0);
}
```
So it is failing starting with extended ascii characters (> 127) :
```
java.lang.AssertionError: for (ascii:128 hex:0x80)
Expected :-62
Actual :128
```
It seems for standard ascii table (hex: 0x00 - 0x7E) `charAt()` produces
identical results as UTF8 encoding. It is expected because UNICODE is identical
to ASCII for first 128 characters (and UTF8 uses single byte for basic ASCII
charset).
The question is how to define Calcite `ASCII` function outside basic ASCII
chars (0-127) ? Or explicitly say behaviour is undefined for non-basic ascii ?
[Transact-SQL](https://docs.microsoft.com/en-us/sql/t-sql/functions/ascii-transact-sql?view=sql-server-2017)
says ASCII works only for [printable
chars](https://en.wikipedia.org/wiki/ASCII#Printable_characters) (0x20- 0x7E)
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