From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtpng3.m.smailru.net (smtpng3.m.smailru.net [94.100.177.149]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dev.tarantool.org (Postfix) with ESMTPS id 87FB4445320 for ; Tue, 28 Jul 2020 14:28:18 +0300 (MSK) Date: Tue, 28 Jul 2020 14:28:14 +0300 From: Mergen Imeev Message-ID: <20200728112814.GA4061@tarantool.org> References: <20200727122429.GA49280@tarantool.org> <0b155dec-3a58-a8fd-3aa8-343bf47e1e69@ocelot.ca> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <0b155dec-3a58-a8fd-3aa8-343bf47e1e69@ocelot.ca> Subject: Re: [Tarantool-discussions] The result type and argument types of the built-in SQL functions. List-Id: Tarantool development process List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Gulutzan Cc: tarantool-discussions@dev.tarantool.org Hi! On Mon, Jul 27, 2020 at 01:39:29PM -0600, Peter Gulutzan wrote: > Hi, > > > On 2020-07-27 6:24 a.m., Mergen Imeev wrote: > > > > Re your table of "current" result data types. I think we must define > "current". > In version 2.4, SELECT TYPEOF(LENGTH('')); returns 'integer'. When I say function result type, I mean this: tarantool> SELECT LENGTH(''); --- - metadata: - name: COLUMN_1 type: integer rows: - [0] ... As you can see, it says that the result type of the LENGTH() function is INTEGER. However, as you said, the type of the value we got is actually UNSIGNED. I will fix this after we come to an agreement. > In version 2.6, SELECT TYPEOF(LENGTH('')); returns 'unsigned'. > In other words, somebody has already made changes, for tarantool-master. > However, I did not document that the return will be 'integer' so this is > a "change in behaviour" but not a "change in documented behaviour". > > And I think we must define 'result type'. > You write that GREATEST etc. return 'scalar'. > But of course SELECT TYPEOF(GREATEST(1,'a')); returns 'string'. > So I assume you do not mean that the result value has the Tarantool 'scalar' > type, you only mean that the result value will be anything that > Tarantool/SQL currently supports. I agree that this is true for the value that was received. However, result type functions are more like column types: tarantool> SELECT GREATEST(1,'a'); --- - metadata: - name: COLUMN_1 type: scalar rows: - ['a'] ... > > Re returning UNSIGNED instead of INTEGER for ...LENGTH(), ROW_COUNT(), etc. > (a) This data type is not standard and is not built-in for most major DBMSs. > Even in MySQL > https://dev.mysql.com/doc/refman/8.0/en/numeric-type-syntax.html > UNSIGNED is an attribute of a data type, as in BIGINT UNSIGNED, not a data > type. > (b) The maximum INTEGER value is the same as the maximum UNSIGNED value, > 18446744073709551615, so the change is not necessary. > (c) Although in Tarantool it is not likely, there are generic programs that > might > be checking whether the result of a function is negative. For example, in > ODBC > https://docs.microsoft.com/en-us/sql/odbc/reference/syntax/sqlrowcount-function?v, > a result of an equivalent of our ROW_COUNT() function can be -1. > ... Therefore I am not enthusiastic about this change. I have no objection here. > > Re returning NUMBER from ROUND(): > You say that the current return is 'integer', but when I try it, > I get 'double'. I think this current behaviour is acceptable. I talked about this: tarantool> SELECT ROUND(1.2345, 2); --- - metadata: - name: COLUMN_1 type: integer rows: - [1.23] ... As you can see, the result is not INTEGER, even if it is written that it is INTEGER. > However, if ROUND(1) returns INTEGER, that is good too -- > the general idea, not a law, would be > "if the result data type can be the same as the input data type(s), > let it be the same". I believe ROUND (a) and ROUND (a, 0) should return INTEGER. I still think that we should consider NUMBER as the return type of a function. However, this does not mean that the type of the values we get as a result will be NUMBER. It will be either INTEGER or DOUBLE. Also, I have an important question: why don't we treat NUMBER the same way we treat SCALAR? Before adding the DOUBLE type, it was possible to say that NUMBER contains INTEGER and real values. So it was in the same position as INTEGER and UNSIGNED right now. However, after adding DOUBLE, all numeric values can be either INTEGER or DOUBLE, so we don't need NUMBER values. I suggest that we allow NUMBER to be the column type, but there should be no NUMBER values. What do you think about this? > > Re types of arguments: > You suggest that TRIM() etc. must have 'string' arguments, > but currently they can be 'varbinary' and I don't see why that is bad. > You suggest that CHAR() must have 'unsigned' argument, > but currently it can be some other type, and well, *maybe* that is bad. > I don't object to strictness, but worry that I might have to document > "sometimes we do an implicit cast, some other times we are strict". I believe the values given as arguments should follow the "IMPLICIT CAST FOR ASSIGNMENT" rules. I plan to use the same mechanism, so I don't see any problems here. For exapmle, ROUND(1.234, 2.5) will work the same as ROUND(1.234, 2). > > Re BLOB instead of string. This is related to the fact that > TRIM() etc. currently do not need to have 'string' arguments, > they can have 'varbinary' arguments. I admit that many (maybe > most) other vendors expect character strings in such cases. > But the standard suggests that something very similar is allowed, > the DB2 manual says it is allowed, > the MariaDB manual is not explicit but here I show it is allowed: > " > mariadb>SELECT HEX(TRIM(X'D0' FROM CAST('Д' AS BINARY))); > OK 1 rows affected (0.0 seconds) > +--------------------------------------------+ > | HEX(TRIM(X'D0' FROM CAST('Д' AS BINARY)))  | > +--------------------------------------------+ > | 94                                         | > +--------------------------------------------+ > " > I believe that Tarantool should continue to allow varbinary arguments. So you mean that all functions that can accept STRING must accept VARBINARY? Do you think we should be thinking about a new type that should contain STRING and VARBINARY the same way NUMBER contains INTEGER and DOUBLE? If you agree with this, can you suggest a name for the new type? > > Re MAP and ARRAY types "in the near future": > I think we must define "near future". > Currently in SQL we do not even have the Lua DECIMAL or UUID data types. > Kirill Yukhin made the issue Implement DECIMAL data type #4415 > on August 8 2019, saying > "After DECIMAL type was introduced to the core, its time to implement this > type in SQL frontend." > We are nearly at August 8 2020, so apparently it takes more than one year to > put > a data type in SQL even though it is already in the core. > ( > So I think that maps and arrays, which I think are more difficult, > will not exist in SQL for two years. I am not worried. It is actually in plans for the next release, however I won't argue with you here. > However, it is interesting to imagine > UPPER(array of strings) -- should we return upper of all elements? > UPPER(map) -- should we return upper of both the key and the value? > and so on. I didn't even thought about these cases. I mean, if function should accept STRING and we will give her an ARRAY, that it should throw an error. After all ARRAY is not STRING. > I believe Lua non-scalar values should be flattened in SQL, > so perhaps the questions can all be avoided. > > Peter Gulutzan > Could you take another look at the tables? Also, here's what the function definition would look like after my patches: tarantool> box.execute([[select "name", "param_list", "returns", "aggregate" from "_func" where "language" = 'SQL_BUILTIN' order by "name" LIMIT 10;]]) --- - metadata: - name: name type: string - name: param_list type: array - name: returns type: string - name: aggregate type: string rows: - ['ABS', ['number'], 'number', 'none'] - ['AVG', ['number'], 'number', 'group'] - ['CEIL', [], 'any', 'none'] - ['CEILING', [], 'any', 'none'] - ['CHAR', ['unsigned'], 'string', 'none'] - ['CHARACTER_LENGTH', ['scalar'], 'integer', 'none'] - ['CHAR_LENGTH', ['scalar'], 'integer', 'none'] - ['COALESCE', ['scalar'], 'scalar', 'none'] - ['COUNT', ['scalar'], 'integer', 'group'] - ['CURRENT_DATE', [], 'any', 'none'] ... I used SCALAR instead of STRING, so we may use VARBINARY instead of STRING. Below is an updated table of function result types. Remember that this is not always the type of the value that we get from the function. However, all values that we receive as a result of executing the function must be of the specified type. FUNCTION NAME CURRENT SUGGESTED abs number number avg number double char string string character_length integer integer char_length integer integer coalesce scalar scalar count integer integer greatest scalar scalar group_concat string string hex string string ifnull integer scalar least scalar scalar length integer integer like integer boolean likelihood boolean scalar likely boolean scalar lower string string max scalar scalar min scalar scalar nullif scalar scalar position integer integer printf string string quote string string random integer integer randomblob varbinary varbinary replace string string round integer number row_count integer integer soundex string string substr string string sum number number total number double trim string string typeof string string unicode string integer unlikely boolean scalar upper string string version string string zeroblob varbinary varbinary Below is an updated table of function argument types. Note that the IMPLICIT CAST FOR ASSIGNMENT rules will be applied before values are passed to the function as arguments. This means that if the function takes STRING and we give it an INTEGER value, we will get an error even before we call the function. FUNCTION NAME TYPES OF ARGUMENTS abs number avg number char* unsigned character_length scalar char_length scalar coalesce scalar count scalar greatest scalar group_concat scalar, scalar hex scalar ifnull scalar, scalar least* scalar length scalar like scalar, scalar, scalar likelihood scalar, double likely scalar lower scalar max scalar min scalar nullif scalar, scalar position scalar, scalar printf* scalar quote scalar randomblob unsigned replace scalar, scalar, scalar round double, unsigned soundex scalar substr scalar, integer, integer sum number total number trim* scalar typeof scalar unicode scalar unlikely scalar upper scalar zeroblob unsigned I still believe that not all functions that accept STRING have to to accept VARBINARY. But that's up to you.