Có 40+ tài liệu thuộc chủ đề "lập trình chuyên nghiệp"
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We emphasize that only past states can be so queried. Even though the trans_stop value is “forever” (chosen to make the queries discussed below easier to write), this must be interpreted as “now.” We cannot unequivocally state what the WDS table will record in the future. transaction-time state tables. Consider the query, “When was it recorded that ‘A1248’ had a...
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172 CHAPTER 5: CHARACTER DATA TYPES IN SQL. Because the equality test has to pad out the shorter of the two strings, you will often find doing a GROUP BY on a VARCHAR(n) has. A length of 1 is returned because it is the length of the shortest string or because it is the length of the first string physically...
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182 CHAPTER 5: CHARACTER DATA TYPES IN SQL. They attempt to preserve the original alphabetical order of the names in the encodings.. But the librarian cannot just attach the author’s name to the. For example, “Smith, John A.” and “Smith, John B.” are not unique until the last letter.. There are several versions of the Cutter tables. The first is...
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192 CHAPTER 6: NULLS: MISSING DATA IN SQL. SQL-92 solved some of the 3VL (three-valued logic) problems by adding a new predicate of the form:. IS NOT FALSE will return TRUE if (age IS NULL) or (gender IS NULL) and the remaining condition does not matter.. Most vendors propagate NULL s in the functions they offer as extensions of the...
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7.2 Storing an IP Address in SQL. If you need to verify them, you can send an e-mail or ping them. In a test conducted in SQL Server, all three methods required about the same amount of time, work, and I/O to return data as a string. 7.2 Storing an IP Address in SQL 203. TINYINT is a one-bit integer...
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the searched deletion uses a WHERE clause like the search condition in a SELECT statement.. 8.1.1 The DELETE FROM Clause. DELETE FROM <table name>. The DELETE FROM clause simply gives the name of the updatable table or view to be changed. Notice that no correlation name is allowed in the DELETE FROM clause. If you had a correlation name, you...
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so it is just shorthand for a particular single row insertion.. In both cases, the optional list of columns in the target table has to be union-compatible with the columns in the query or with the values in the VALUES clause. Any column not in the list will be assigned NULL or its explicit DEFAULT value.. In theory, an insert...
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The result of the UPDATE cannot be determined. The value of the column will depend upon either order of insertion, (if there are no clustered indexes present), or on order of clustering (but only if the cluster is not fragmented).. FOR EACH row IN the Transactions table DO IF working row NOT IN Master table. In the 1950s, we would...
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non- NULL values is defined by Table 10.1, where Degree means the number of columns in the row expression.. Table 10.1 Cases Where a Row Is a Mix of NULL and non- NULL Values. R IS R IS NOT NOT R IS NOT R IS NOT Expression NULL NULL NULL NULL. NULL TRUE FALSE FALSE TRUE No NULL FALSE TRUE...
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CASE WHEN <value exp #1>. A CASE expression is very useful with a GROUP BY query. Aggregate functions remove NULL s before they perform their operations, so the order of execution might be different in the ELSE 0 and the ELSE NULL versions.. The previous example shows the CASE expression inside the aggregate function. it is possible to put aggregate...
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262 CHAPTER 12: LIKE PREDICATE. is used in the <pattern>. 12.1 Tricks with Patterns. The wildcards can be inserted in the middle or beginning of a pattern. Thus, ‘B%K’ will match ‘BOOK’, ‘BLOCK’, and ‘BK’, but it will not match ‘BLOCKS’.. In the case of ‘BLOCKS’, the initial ‘B’ would be an exact match and the parser would continue. ‘L’,...
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BETWEEN and OVERLAPS Predicates. The BETWEEN predicate works with scalar range limits. the OVERLAPS predicate looks at two time periods (defined either by start and end points or by a starting time and an INTERVAL ) to see if they overlap in time.. 13.1 The BETWEEN Predicate. The predicate <value expression>. [NOT] BETWEEN <low value expression>. AND <high value expression>....
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What we want is the part of the Guests interval that is inside the Celebrations interval.. guest_name celeb_name entered exited. 'Dorothy Gale' 'Apple Month Dorothy Gale' 'Apple Month Dorothy Gale' 'Garlic Festival Dorothy Gale' 'Garlic Festival Dorothy Gale' 'St. 'Dorothy Gale' 'St. Fred's Day Dorothy Gale' 'Year of the Prune Dorothy Gale' 'Year of the Prune Indiana Jones' 'Apple Month...
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292 CHAPTER 14: THE [NOT] IN() PREDICATE. FROM JohnsBook AS J1 WHERE NOT EXISTS (SELECT. The NOT IN() version has to test all the values in the subquery table for inequality.. Many SQL implementations will construct a temporary table from the IN() predicate subquery, if it has a WHERE clause, but the temporary table will not have any indexes. 14.2...
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302 CHAPTER 15: EXISTS() PREDICATE. SELECT P1.emp_name. FROM Personnel AS P1 WHERE P1.birthday NOT IN. (SELECT C1.birthday FROM Celebrities AS C1. WHERE C1.birth_city = 'New York');. FROM Personnel AS P1 WHERE NOT EXISTS (SELECT. FROM Celebrities AS C1. WHERE C1.birth_city = 'New York' AND C1.birthday = P1.birthday);. The subquery will be empty for every employee in the NOT EXISTS predicate...
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When you get a single FALSE result, the whole predicate is FALSE . <comp op>. <comp op>. This makes sense, because every row comparison test in the expansion would return UNKNOWN , so the series of OR and AND operators would behave in the usual way.. However, <value expression>. But most people have lots of trouble seeing why the ALL...
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2 'Smyth' 'F' 17 | 8 'A' 3 'Smoot' 'F' 16 | 1 'A' 3 'Smoot' 'F' 16 | 2 'B' 3 'Smoot' 'F' 16 | 3 'C' 3 'Smoot' 'F' 16 | 4 'D' 3 'Smoot' 'F' 16 | 5 'A' 3 'Smoot' 'F' 16 | 6 'A' 3 'Smoot' 'F' 16 | 7 'A' 3 'Smoot' 'F' 16...
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SELECT F1.fruit, F1.score, FROM Foobar AS F1. ORDER BY F1.score DESC;. ORDER BY F1.score DESC, F1.fruit ASC;. But this is not what we wanted—the order within fruits has been destroyed. SELECT F1.fruit, F1.score FROM Foobar AS F1. ORDER BY F1.fruit ASC, F1.score DESC;. But this is still not what we wanted—the order within scores has been destroyed. SELECT F1.fruit, F1.score,....
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SELECT sup_id, sup_name, (SELECT COUNT. WHERE Suppliers.sup_id = Orders.sup_id) FROM Suppliers;. SELECT sup_id, sup_name, COUNT. FROM Suppliers LEFT OUTER JOIN Orders ON Suppliers.sup_id = Orders.sup_id GROUP BY sup_id, sup_name;. 17.2.2 NULLs and OUTER JOINs. The NULL s generated by the OUTER JOIN can occur in columns derived from source table columns that have been declared to be NOT NULL ....
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The INNER JOIN operator did get to be popular. Additionally, it is a binary operator, and programmers are used to binary operators—add, subtract, multiply, and divide are all binary operators. Consider this statement, which would have been written in the traditional syntax as:. WHERE Foo.y BETWEEN Bar.x AND Flub.z;. With the infixed syntax, I can write this same statement in...