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Fix SUBSTRING with a non-positive start position #2521

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Fix SUBSTRING with a non-positive start position #2521

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20 changes: 18 additions & 2 deletions src/55functions.js
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Original file line number Diff line number Diff line change
Expand Up @@ -186,8 +186,24 @@ stdlib.SUBSTRING =
stdlib.SUBSTR =
stdlib.MID =
function (a, b, c) {
if (arguments.length == 2) return und(a, 'y.substr(' + b + '-1)');
else if (arguments.length == 3) return und(a, 'y.substr(' + b + '-1,' + c + ')');
if (arguments.length == 2)
return und(
a,
'(__alasql_tmp=(' +
b +
'),__alasql_tmp==0?"":(__alasql_tmp<0?(y.length+__alasql_tmp<0?"":y.substr(y.length+__alasql_tmp)):y.substr(__alasql_tmp-1)))'
);
else if (arguments.length == 3)
return und(
a,
'(__alasql_tmp=(' +
b +
'),__alasql_tmp==0?"":(__alasql_tmp<0?(y.length+__alasql_tmp<0?"":y.substr(y.length+__alasql_tmp,' +
c +
')):y.substr(__alasql_tmp-1,' +
c +
')))'
);
};

stdfn.REGEXP_LIKE = function (a, b, c) {
Expand Down
35 changes: 35 additions & 0 deletions test/test-substring-negative-start.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,35 @@
if (typeof exports === 'object') {
var assert = require('assert');
var alasql = require('..');
}

describe('SUBSTRING with non-positive start position', function () {
it('follows MySQL semantics for start = 0', function () {
assert.strictEqual(alasql("SELECT VALUE SUBSTRING('abcdef', 0, 3)"), '');
assert.strictEqual(alasql("SELECT VALUE SUBSTRING('abcdef', 0)"), '');
});

it('follows MySQL semantics for a negative start (counts from the end)', function () {
assert.strictEqual(alasql("SELECT VALUE SUBSTRING('abcdef', -1, 3)"), 'f');
assert.strictEqual(alasql("SELECT VALUE SUBSTRING('abcdef', -2, 3)"), 'ef');
assert.strictEqual(alasql("SELECT VALUE SUBSTRING('abcdef', -2)"), 'ef');
assert.strictEqual(alasql("SELECT VALUE SUBSTRING('abcdef', -6)"), 'abcdef');
});

it('returns empty when a negative start reaches past the string start', function () {
assert.strictEqual(alasql("SELECT VALUE SUBSTRING('abcdef', -7, 3)"), '');
assert.strictEqual(alasql("SELECT VALUE SUBSTRING('abcdef', -10, 3)"), '');
assert.strictEqual(alasql("SELECT VALUE SUBSTRING('abcdef', -7)"), '');
});

it('leaves positive start positions unchanged', function () {
assert.strictEqual(alasql("SELECT VALUE SUBSTRING('abcdef', 1, 3)"), 'abc');
assert.strictEqual(alasql("SELECT VALUE SUBSTRING('abcdef', 2, 3)"), 'bcd');
assert.strictEqual(alasql("SELECT VALUE SUBSTRING('abcdef', 4)"), 'def');
});

it('applies the same rules to the SUBSTR and MID aliases', function () {
assert.strictEqual(alasql("SELECT VALUE SUBSTR('abcdef', 0, 3)"), '');
assert.strictEqual(alasql("SELECT VALUE MID('abcdef', -2, 3)"), 'ef');
});
});