Is there a "diff" function in Oracle PL/SQL, that shows differences between two text strings? - oracle

Question

We have logging tables in our Oracle database that show old and new values when changes are made to certain data fields. One of these fields is a SQL_TEXT field (for running reports via dynamic SQL).
For example:
CREATE TABLE schema1.rpt_sql_log (
rpt_id NUMBER(9), -- surrogate key of report
chg_id NUMBER(9), -- change number of query for this rpt_id
old_sql_txt VARCHAR2(2000), -- old report SQL statement
new_sql_txt VARCHAR2(2000) -- new report SQL statement
);
INSERT INTO schema1.rpt_sql_log VALUES (
1,
2,
'SELECT emp_id, dept_id, salary FROM emp ORDER BY emp_id',
'SELECT emp_id, dept_nm, salary FROM emp e INNER JOIN dept d ON e.dept_id = d.dept_id ORDER BY emp_id'
);
COMMIT;
Our analyst ordinarily would export these fields to 2 separate text files and then open them in BeyondCompare, UltraCompare, or WinMerge. They have asked if it is possible to do this textual comparison/diff directly in a query (i.e., is there a built-in diff function). To the best of my knowledge, no such built-in function exists.
My question is this: is there already a "diff-like" function available online that mimics the output of a Myers diff algorithm (i.e., something that highlights or <tag>s the changes, as one might see in Git or TortoiseSVN)

Answer 1

To my knowledge, there is no such built-in PL/SQL function to do so.
However, using this JavaScript code which describes a diff function that adds and tags and the MultiLingual Engine capabilities of the 21c Oracle database release (which allows you to create stored procedures that can execute JavaScript code); you could go with such an approach:
set define off
set serveroutput on size unlimited
DECLARE
ctx DBMS_MLE.context_handle_t := DBMS_MLE.create_context();
codeSnippet clob ;
result clob;
BEGIN
codeSnippet := q'~
/*
* Javascript Diff Algorithm
* By John Resig (http://ejohn.org/)
* Modified by Chu Alan "sprite"
*
* Released under the MIT license.
*
* More Info:
* http://ejohn.org/projects/javascript-diff-algorithm/
*/
function escape(s) {
var n = s;
n = n.replace(/&/g, "&");
n = n.replace(/</g, "<");
n = n.replace(/>/g, ">");
n = n.replace(/"/g, """);
return n;
}
function diffString( o, n ) {
o = o.replace(/\s+$/, '');
n = n.replace(/\s+$/, '');
var out = diff(o == "" ? [] : o.split(/\s+/), n == "" ? [] : n.split(/\s+/) );
var str = "";
var oSpace = o.match(/\s+/g);
if (oSpace == null) {
oSpace = ["\n"];
} else {
oSpace.push("\n");
}
var nSpace = n.match(/\s+/g);
if (nSpace == null) {
nSpace = ["\n"];
} else {
nSpace.push("\n");
}
if (out.n.length == 0) {
for (var i = 0; i < out.o.length; i++) {
str += '<del>' + escape(out.o[i]) + oSpace[i] + "</del>";
}
} else {
if (out.n[0].text == null) {
for (n = 0; n < out.o.length && out.o[n].text == null; n++) {
str += '<del>' + escape(out.o[n]) + oSpace[n] + "</del>";
}
}
for ( var i = 0; i < out.n.length; i++ ) {
if (out.n[i].text == null) {
str += '<ins>' + escape(out.n[i]) + nSpace[i] + "</ins>";
} else {
var pre = "";
for (n = out.n[i].row + 1; n < out.o.length && out.o[n].text == null; n++ ) {
pre += '<del>' + escape(out.o[n]) + oSpace[n] + "</del>";
}
str += " " + out.n[i].text + nSpace[i] + pre;
}
}
}
return str;
}
function randomColor() {
return "rgb(" + (Math.random() * 100) + "%, " +
(Math.random() * 100) + "%, " +
(Math.random() * 100) + "%)";
}
function diffString2( o, n ) {
o = o.replace(/\s+$/, '');
n = n.replace(/\s+$/, '');
var out = diff(o == "" ? [] : o.split(/\s+/), n == "" ? [] : n.split(/\s+/) );
var oSpace = o.match(/\s+/g);
if (oSpace == null) {
oSpace = ["\n"];
} else {
oSpace.push("\n");
}
var nSpace = n.match(/\s+/g);
if (nSpace == null) {
nSpace = ["\n"];
} else {
nSpace.push("\n");
}
var os = "";
var colors = new Array();
for (var i = 0; i < out.o.length; i++) {
colors[i] = randomColor();
if (out.o[i].text != null) {
os += '<span style="background-color: ' +colors[i]+ '">' +
escape(out.o[i].text) + oSpace[i] + "</span>";
} else {
os += "<del>" + escape(out.o[i]) + oSpace[i] + "</del>";
}
}
var ns = "";
for (var i = 0; i < out.n.length; i++) {
if (out.n[i].text != null) {
ns += '<span style="background-color: ' +colors[out.n[i].row]+ '">' +
escape(out.n[i].text) + nSpace[i] + "</span>";
} else {
ns += "<ins>" + escape(out.n[i]) + nSpace[i] + "</ins>";
}
}
return { o : os , n : ns };
}
function diff( o, n ) {
var ns = new Object();
var os = new Object();
for ( var i = 0; i < n.length; i++ ) {
if ( ns[ n[i] ] == null )
ns[ n[i] ] = { rows: new Array(), o: null };
ns[ n[i] ].rows.push( i );
}
for ( var i = 0; i < o.length; i++ ) {
if ( os[ o[i] ] == null )
os[ o[i] ] = { rows: new Array(), n: null };
os[ o[i] ].rows.push( i );
}
for ( var i in ns ) {
if ( ns[i].rows.length == 1 && typeof(os[i]) != "undefined" && os[i].rows.length == 1 ) {
n[ ns[i].rows[0] ] = { text: n[ ns[i].rows[0] ], row: os[i].rows[0] };
o[ os[i].rows[0] ] = { text: o[ os[i].rows[0] ], row: ns[i].rows[0] };
}
}
for ( var i = 0; i < n.length - 1; i++ ) {
if ( n[i].text != null && n[i+1].text == null && n[i].row + 1 < o.length && o[ n[i].row + 1 ].text == null &&
n[i+1] == o[ n[i].row + 1 ] ) {
n[i+1] = { text: n[i+1], row: n[i].row + 1 };
o[n[i].row+1] = { text: o[n[i].row+1], row: i + 1 };
}
}
for ( var i = n.length - 1; i > 0; i-- ) {
if ( n[i].text != null && n[i-1].text == null && n[i].row > 0 && o[ n[i].row - 1 ].text == null &&
n[i-1] == o[ n[i].row - 1 ] ) {
n[i-1] = { text: n[i-1], row: n[i].row - 1 };
o[n[i].row-1] = { text: o[n[i].row-1], row: i - 1 };
}
}
return { o: o, n: n };
}
var bindings = require("mle-js-bindings");
var string1 = bindings.importValue("string1");
var string2 = bindings.importValue("string2");
bindings.exportValue("result", diffString(string1,string2)); ~';
dbms_mle.export_to_mle(ctx, 'string1', 'The red brown fox jumped over the rolling log.');
dbms_mle.export_to_mle(ctx, 'string2', 'The brown spotted fox leaped over the rolling log');
DBMS_MLE.eval(ctx, 'JAVASCRIPT', codeSnippet);
DBMS_MLE.import_from_mle(ctx, 'result', result);
DBMS_OUTPUT.put_line(result);
DBMS_MLE.drop_context(ctx);
END;
/
Running the code above using SQLcl, gives me:
The <del>red </del> brown <ins>spotted </ins> fox <del>jumped </del><ins>leaped
</ins> over the rolling <del>log.
</del><ins>log
</ins>
PL/SQL procedure successfully completed.
SQL>