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In SQL, the unique keys have a UNIQUE constraint assigned to them in order to prevent duplicates (a duplicate entry is not valid in a unique column). Alternate keys may be used like the primary key when doing a single-table select or when filtering in a where clause, but are not typically used to join multiple tables.
Parts 1 and 2 are the basis for part 13 of the SQL standard, SQL Routines and Types Using the Java Programming Language (SQL/JRT). "SQLJ" is commonly used to refer to just SQLJ part 0, usually when it is contrasted with other means of embedding SQL in Java, like JDBC .
A numeric character reference refers to a character by its Universal Character Set/Unicode code point, and a character entity reference refers to a character by a predefined name. A numeric character reference uses the format &#nnnn; or &#xhhhh; where nnnn is the code point in decimal form, and hhhh is the code point in hexadecimal form.
Characters are searchable by Unicode character name, and the table can be limited to a particular code block. [7] Starting with Windows 10 Microsoft Windows also contains so called "emoji keyboard". It can be started by holding down the Windows key (the one with the Windows symbol on it) and hitting the period or semicolon key.
Under Windows, the Alt key is pressed and held down while a decimal character code is entered on the numeric keypad; the Alt key is then released and the character appears. The numerical code corresponds to the character’s code point in the Windows 1252 code page, with a leading zero; for example, an en dash (–) is entered using Alt+0150 ...
Category "Cc" control codes can serve a variety of purposes, not limited to format effectors: for example, the default ASCII C0 set includes six format effectors (BS, HT, LF, VT, FF and CR), ten transmission controls, four device controls, four information separators and eight other control codes. [4] Most of these characters play no explicit ...
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special characters that are not available in the limited character set are stored in the form of a multi-character code; there are usually two or three equivalent representations, e.g. for the character € the named character reference € and the decimal character reference € and the hexadecimal character reference €. The edit ...